Update: Read the more recent article about the “We need workers” problem.
This article from Gameplay Scripter Jason Halvorson details the system by which SimCity enrolls Sims for jobs and distributes them throughout the city. It’s an interesting article and an in-depth, behind-the-scenes look at the mechanics of the game. It involves a Worker Request Agent, which essentially acts as a recruiter for local businesses.
However, I would say that based on my own experience, it represents a best-case scenario. For example, I recently had a city with hundreds of unemployed homeless people roaming the streets, meanwhile jobs were going wanting, even with the relatively large number of inbound commuters.