I have an office in my home and that's where I do all my work. I've got enough extra desk space so that I don't have to take paperwork out of the office to work on and can wheel around between all the various parts (computer setup, workdesk, printer station) with minimal effort (always important

).
I used to just have a portion of my apartment for my office, but I found it very difficult to separate out the parts of my life doing so. I found myself working way too many hours because no matter what time of day it was or what I had just finishing doing (watching a movie, for example), I'd see the darn computer and say to myself "I'll just log on and do a little work" and next thing I knew it was 4 am in the morning and I had to get to my "real" job at 8 am.
It helped me a lot once I got a separate room for the office, as I could close the door when I was done for the day and put it out of my mind. It really helped me to organize myself better, I think, too.