In The Sims 2, once you had all the boxes ticked so to speak, then boom: promoted. This is how so many of us got all those great career rewards! You max out all of your Sim's skills, make a bunch of friends, then start a new job. Almost immediately, your Sim is promoted to level 6 or whatever, and you get the reward. Quit that job, start another one, lather rinse repeat.
Not so with The Sims 3!