I'm often a hacker in my spare time. For that reason I have a small collection of computers and computer parts at home, including infrastructure to maintain and debug issues with them, often while experimenting with some new software I'm writing (e.g. terminal server, remote power switches, ethernet switches, UPSs, A/C, etc). I repair and/or build new computers from time to time as well as admire unusual computers, such as S/390 (or their older cousins, System/360s), VAX, PDP, etc. Or sometimes large Sun servers, like E4500s or the newer Fire series. Unfortunately I don't have any room for those, so usually it's friends who have them (and they're really only cool to observe, not so much getting them to do something). But I do have some smaller ones, like an SGI Indy, a Sun Blade 100, & a DEC Alpha PWS. One day I'd like to own an oscilloscope or preferably a nice logic analyzer, but those are currently out of my budget. As it is, I've been doing this stuff for about six years, and it is now obvious to me that at some point I'm probably going to want a different hobby that doesn't reqiure so much brain power.
When I'm not experimenting with computers (or to a lesser extent electronics), I like playing sports of all kinds. In recent years, that's usually one of: racquetball, volleyball, ultimate frisbee, basketball, water polo, snowmobiling, skiing, water skiing, etc etc. I really don't have enough sports in my life as it is. I hope to change that in the near future, though.
I also like to play video games, watch movies, etc. Hardly surprising, right?
As for why.. well, the age-old motivations: fun, and that wonderful pang you get when you create something (whether it is new, useful, or not)!
And frankly, I think the best hobbies to have are the ones where you create something new... not the ones where you are just a consumer.
