[bumby]

The short answer is "inevitable disclosure doctrine" that prevents you from working for a competitor if it's inevitable that you will disclose trade secrets. It's a sticky wicket for engineers.

However, this might be confusing different issues. My comment was specific to using NDAs/non-competes to protect trade secrets. This is different from merely using them to prevent poaching by competitors. In cases were there isn't inevitable disclosure, I think it's much less likely that a non-compete would be enforced in court.