[bdickason]

I'm a product manager by day and I generally have a hobby that I throw myself into on weekends that may/may not be work related. Currently, for example, I alternate between coding (something I don't get to do at work) and playing video games like TF2. Once my wife gets home, however, we do stuff like rooftop gardening, going out to dinner, etc.

My past 'obsessions' (as she calls them) have included DJing 3-4 nights per week, producing Disco music, playing world of warcraft, and doing kickboxing/jujitsu.

In short, do what you feel passionate about whether it's work-related or not. If you feel like you should be spending time with your friends, go for it! If you feel like doing startup stuff, do that.

As long as it's what fuels you, work-related stuff is not a bad thing.