Possible Duplicate:
How can I keep from getting addicted to SO?
Looking up answers to questions on Stack Overflow obviously is benefical for your employer, but it's very, very tempting, to keep asking questions, submitting answers to random questions just to to earn points, and get familiar with Stack Overflow (and Stack Exchange). I guess it's OK if you do that for questions/answers that are relevant for the company you work for.
So maybe a possibility is to determine whether it is relevant or not, and wait if you get home and still want to post/answer in your free time.