Hmm I also have that in my Dutch contract. I really don't like the way my current employer handles their market and I'm eager to do it right myself (I feel that with the right technologies I could really build something nice myself.) This part of my contract has kept me from it (the "we own what you make at any time of the day"-clause). I do understand the clause though, it's just to easy to claim you made up some valuable IP outside of office hours. Maybe I should keep a log regarding the actual dev work...

With respect to the non-compete clause, it says in my contract that they can keep me from going to a competitor for a year, but they'll pay me for that year. I wonder if they'd ever enforce this.