You can also ask your employer for an explicit exemption for whatever you're working on. I've had all of my side projects cleared before doing serious work on them (although that did kill one project, since it was too close to something my company was doing)
or you can live in california, where all these kinds of agreement are more likely to be un-enforcable. Maybe that's the reason that so many startups are here?
Be careful just assuming they are unenforceable. Non-compete agreements are, but if your company can show that they have any "actual or anticipated" research, development or plans in this area things are up in the air.
