Character Development: Yes, it even applies to people who aren't playing characters. In the show's formative days, Adam was more lively than Jamie, yes, but certainly far more reserved than you see him in future episodes. Apparently as he grew hair, his personality became more vibrant (he started the show with a very short haircut and no beard).
Several other cases throughout the series. For example, in the first episode of season two, Adam had trouble hitting his target with the gun provided (justified as he was a novice shooter at the time). This gave him an early reputation as a poor shot, which stuck with him until the "Shooting the Scope" myth showed his aim had improved significantly. His shooting skills have since improved to the point that he now seems to be better with a pistol than Jamie.
Crouching Moron, Hidden Badass: Fails onscreen more often than he succeeds, and Jamie usually designs better rigs, but Adam often replicates props from movies using only stills from the film or even occasionally gets the actual props themselves.
Also, according to Jamie in one of the web videos, Adam is widely known in the special effects business for being able to make good models and machines extremely quickly.
Forgets To Eat: According to Jamie. Which means that Jamie's suggestion that Adam "go eat a cookie" during the ping-pong ball flotation myth was actually not a joke, since Adam is known to forget to eat and get low blood sugar, which makes him cranky.
For Science!: "I ate a radio for science" is just one example of what he will do in the name of science.
Teeth-Clenched Teamwork: He and Jamie have made it clear that they have a good deal of respect for each other but on an interpersonal level they annoy each other to no end and do not hang out after work. Occasionally, this makes it past the editing and we see Adam annoyed at Jamie's fussiness and methodical approach.
Bulletproof Fashion Plate: Multiple members of the cast and crew have expressed bafflement at how he always manages to keep his white shirt spotless. Turns out he actually was using (and continues to use) a special clothing treatment that basically makes any fabric it's applied to impervious to most liquids.
Expansion Pack Past: Provides the page quote. Adam frequently provides details on Jamie's past to the point it's almost a Multiple-Choice Past—apparently Jamie is descended from a line of "track-straighteners" dating back to the middle ages, worked for the mob, and may be an alien and/or over two thousand years old. Or Theodore Roosevelt, to whom he bears a pretty uncanny resemblance. His real past, though not as funny, is genuinely awesome: he ran away from home at 14 and hitchhiked across the U.S., has a degree in Russian linguistics, and has been, in alphabetical order, an animal wrangler, a boat captain, a chef, a pet shop owner, a scuba divemaster, and a wilderness survival instructor. And that's not even a complete list.
Funny Character, Boring Actor: The main reason Jamie brought Adam in on the show is because he is naturally The Stoic and uninteresting by himself. Adam's high energy level and their good working relationship manages to mask this on camera, but they've also said the editing makes Jamie seem more quick-witted and eloquent than he really is.
Hates Being Touched: Has no problems with handshakes, but Jamie apparently doesn't like being hugged.
Honorary Uncle: Considering Adam's description of the team as "like family", it is fitting that Jamie has been occasionally referred to as "Uncle Jamie" — twice by Adam, of all people ("Ancient Death Ray", 2004 — during the "What is Bulletproof?" segment, and again during "Tablecloth Chaos" in 2010) and also by Robert Lee, the narrator ("Viral Hour", 2008, during the Sawdust cannon section.).
Human Alien: "This crater is about the same size as the one left by Jamie when he first came to Earth." — Adam Savage
Limited Wardrobe / Iconic Outfit: Rarely will you find Jamie not wearing his white shirt and beret. When he and Adam meet Barack Obama Adam is in a nicely tailored suit and Jamie is in the same clothes he always wears.
Memetic Badass: If he isn't among the fanbase, he sure as hell is among the cast and crew, who regularly describe him as "abnormally strong". In the "Car Cling" myth, Adam even cites a number of the Bad Ass things that Jamie's done over the course of the show, such as climbing up the side of a building using only a rope, and bashing down a door with his shoulder. invoked
Adam: It's been said that this crater is not unlike the one left by Jamie when he first came to Earth.
The Stoic: Especially in earlier episodes, where Jamie calling out Adam and the producers on deliberately trying to provoke him was practically a Running Gag.
He seems to play up his stoic image for a laugh in the men versus women episode. When the MythBusters are told to show various emotions for a test to see who can read emotions better. Jamie says the emotion... then keeps his face completely expressionless.
Not So Stoic: Has gotten more prone to joking around and visibly enjoying himself during myth testing as the show has gone on.
This is perhaps a case of Character Development as with Adam since it's been mentioned that early on in the show, he was not particularly comfortable on camera and took the job fairly seriously. With time and exposure, it's possible he's gotten comfortable with the idea that for a fairly light hearted show, it allows for a fairly serious platform for science and education.
A more serious take on this trope appeared in the second duct tape episode, where they made a bridge using only duct tape. It was revealed then that Jamie is acrophobic (a fact that had been briefly mentioned in the Hammer Bridge Drop myth back in season one), and his voice increasingly betrays his fear as he continues to test the bridge, even as a) he's wearing a safety rig, and b) Adam already successfully crossed under the same circumstances. Becomes a heartwarming/awesome moment when he finally makes it and Adam announces, "Ladies and gentlemen, they are made of brass, Mr. Jamie Hyneman."
Teeth-Clenched Teamwork: He and Adam have made it clear that they have a good deal of respect for each other but on an interpersonal level they annoy each other to no end and do not hang out after work. When this makes it past editing, we notice that Jamie is annoyed by Adam's showmanship, competitiveness and occasionally sloppy work.
Robosexual: He was once asked, under polygram, if he ever considered making a 'female robot'. He has.
In an episode, the gang encounters a bomb-disposal robot. Grant is VERY impressed, to the point where Kari and Tory jokingly tries to set them up. Grant, playing along, awkwardly tries to flirt with it.
The Smart Guy: He builds the robots and is the closest to a stereotypical nerd.
Ms. Fanservice: Sometimes, as she's prone to wearing tight-fitting tank-tops. Also, her first appearance on the show was dressing in spandex leggings to have her butt laser-scanned for computer modeling. In some specific episodes she is also seen in a "slave girl" outfit in the Goldfinger body paint revisit, wearing a bikini when out on a boat in the Bahamas and the show used her FHM photos for one of the myths (Diet Coke and Mentos).
Suspiciously Similar Substitute: Jessi Combs is a thin blonde, has some tattoos, is proficient in welding and vehicle mechanics, and even copied Scottie's shipping-container-into-ramp trick that she did for the 2nd attempt at the JATO Rocket Car myth.
Tim Taylor Technology: She rigged a nitro-boost system into a car standing in for a Lamborghini (proper dimensions at a lesser cost but not fast enough normally) in the myth of a car skipping across a lake.
Made of Iron/Made of Plasticine: Buster has seen more punishment than any other crash test dummy ever will, and even though the Mythbusters have made him more durable to withstand the forces they put him through, he still ends up in bits more often than not.