I had an offer to work at Microsoft just out of college. I was seriously considering the offer until I saw the draconian anti-employee non-compete they wanted me to sign. I told the recruiter that I didn't feel comfortable signing such an agreement since Microsoft works in so many different areas that there was no way to avoid some sort of conflict. I was assured by the recruiter that they don't usually enforce the agreement. Maybe that is generally true, but this ruling definitely proves that they will enforce it on occasion. Instead I ended up with a different company in CA where such draconian non-competes are illegal and most companies don't even attempt to get you to sign one.
I should also add that not all non-competes have to be as evil as Microsoft's. One company I had an offer for had a similar non-compete but it had a clause that if they decide to enforce it as long as it's in force and you're looking for other gainful employment they would continue to pay you your salary until the non-compete expired. I felt that this policy was more than fair since it allowed the company to decide how important enforcing the non-compete was and didn't have such negative consequences for you as an employee should they choose to enforce it. I personally feel all non-competes should include such a clause otherwise I would NEVER consider signing one.