Ed appears to be a terrible employee due to his lack of common sense— he gives a customer nothing but a bun when he asks for a Good Burger "with nothing on it," for example. Kurt, however, mentions that Ed has worked for Good Burger the last three years. It's possible that he kept his job simply by being so loyal to the restaurant, which probably means he's punctual, willing to work when others might not be, and doesn't complain.
It's also mentioned that Ed hasn't been given a raise during his entire time working at Good Burger. This is presumably because he hasn't earned it. As soon as he nets the store huge profits with his sauce, Mr. Baily gives him a raise in the form of a cut from every Good Burger the store sells.
The customer who orders a Good Burger with nothing on it threatens to report Ed's name to the manager. Ed claims, however, that the manager already knows his name. Damn right he does, as many times as customers probably have reported Ed to Mr. Baily due to his ineptitude. This might be what Ed meant (that customers have repeatedly given his name to Mr. Baily).
Mondo Burger's additive enlarges the burger after heating. Too much additive causes the burger to explode. Boyle's Law (PV=nRT) would suggest that the additive, then, turns into a gas upon heating. This is because the temperature (T) and gas constant (R) are constant, the amount of chemical in the gaseous state (n) is the independent variable, the volume (V) most readily changes as a dependent variable, but when the volume can't increase any more the resultant change in pressure (P) causes a burger explosion.
This also explains why the dog wouldn't eat the Mondo Burger: if it simply added meat-mass then it would smell and taste like real meat because it would be real meat.
Kurt's cult leader-like speech to his employees about how "from now on, your LIFE is Mondo Burger/forget your friends and family" makes a lot more sense when you remember that he was trusting them with a secret about Mondo Burger that would land him in prison if it ever got out. Makes you wonder why he didn't try harder to stop Roxanne from quitting.
When Mondo Burger begins to implode, the customers are bewildered as to what's going on. Since the movie is set in California, you'd think they would assume it was an earthquake.
Ed proves himself as Obfuscating Stupidity. He reads the contract, and while doing so points to specific spots as though he were actually understanding it. Further, Dexter tells Ed exactly what the contract states: 20% of Ed's sauce-based profits goes to Ed; the other 80% goes to Dexter. Ed, then, probably knew full well that he was being ripped off by Dexter (20 cents for every 10 burgers sold). And he still signed the contract, in order to make a friend and help someone in need.
Did he sign the contract before or after Dexter realized Ed caused the car crash? If he did so after, then maybe he signed out of guilt and/or to help Dexter pay off the repair bill more quickly.