I work from home 3-5 days a week. My advisor would rather have me in the office more often - so much that he put a computer in my office the other day! - but I'll still work at home at least 2 days a week I think. You have to be motivated, I think - to be able to get enough done. For me, it's easier and more relaxing to work in my pajamas on my couch than sitting in a stuffy office! Good luck!