A Crack in Time is perhaps the only game to feature two of Mario and Luigi's voice actors at once: Charles Martinet as Orvus and Marc Grauenote The plumbers in Hotel Mario... you did not expect that, did you? as Mr. Zurkon.
One of the subtitles considered for A Crack in Time was "Clock Blockers". Needless to say, Sony's legal department said "no".
Armin Shimerman (Dr. Nefarious), Richard Steven Horvitz (the Zoni, Pollyx) and David Kaye (Clank) all worked on A Crack in Time, but also provided the voices of characters from Psychonauts, in order: Razís dad, Raz, and Ford Cruller/The Hideous Hulking Lungfish of Lake Oblongata. Amusingly, Shimerman and Horvitz play allies (however briefly) who become enemies in ACIT, which is (loosely) reversed in Psychonauts.
Ratchet was voiced by Mike Kelley in the first game, but was replaced by James Arnold Taylor for Going Commando onwards (though Kelley's voice was used for Ratchet's battle grunts up until Quest for Booty).
The Plumber was originally voiced by Neil Flynn, but was replaced by Jess Harnell after the transfer to PS3. Flynn did return for Secret Agent Clank, however, but only because it was in an alternate continuity.
What Could Have Been: Ratchet went through several different early designs, one of which was even shorter than he already is, and one that was more cat-like. Clank was originally supposed to be three floating spheres, each with an individual personality, but they ultimately decided it would be too difficult to keep the personalities from competing for attention (not to mention they looked aesthetically terrible on Ratchet) so they condensed them all into Clank. There were also some scrapped weapons that didn't make the cut in the original game, most notably a Drill weapon called the Revolverator that was difficult to program and was simply not enjoyable to use (but it makes a cameo in-game as a prop used by a miner), and a Giganto Ray and Shrink-O-Ray weapon that only appeared in promo images for the game; some of these scrapped weapons managed to sneak onto the cover of the original game. The Hydrodisplacer and Hologuise gadgets also had different designs early on. There was also a scrapped Hydra miniboss fight for Pokitaru, which was replaced with Ratchet just fighting the local wildlife on a boat. The most notable cut from the original game was an unnamed "Water Planet", complete with it's own boss battle, as well as a Jetski gadget for that level.
The infamous Thug Leader giant robot fight late in Going Commando was originally going to be a chase sequence, with Ratchet using a speeder while shooting back at the robot while it was chasing them throughout the city, but it was cut due to being out of place in the game, and lacking any strong firepower. There was also a scrapped weapon called the Hound of Doom, and a turret upgrade for the Hydropack called the Gunsled that allowed it to shoot underwater. The Youtube developer commentary for Going Commando revealed that the Rift Inducer weapon was originally planned to debut in this game and not Up Your Arsenal, but they either weren't able to get it working right or it was too overpowered at the time.
Up Your Arsenal was originally going to have racing courses, including one on Florana using the Turbo Slider, but this was cut due to development time constaints, but one of the unfinished tracks can be played via the Insomniac Museum, and a voice clip left in the game makes an offhand mention of the scrapped race course. The Hovership and Turboslider also had substantially different designs early on. There were also two beta Qwark vid-comics that didn't make the cut, but are still playable.