Just like pretty much everyone else, I had to sign an IP - waivey - thingy when I started working where I am. I of course read all the fine print, and it was relatively non-fascist. The one section I objected to was the clause that said all the work I created while employed belonged to the employer.

I mentioned my objection to this right away (I was reading the contract while in the presence of one of the directors of the company), and the director was perfectly happy to amend the clause to read something like "any work done while in the employ of the company AND within the scope of the employment..."

This suited both parties, because on the one hand the company couldn't claim IP on any personal work of mine or any OSS involvement, and on the other hand I couldn't memorize how a part of the software I'm building works, go home and rewrite it, and claim it as my own.