I have it written in my agreement that I charge a 25% premium for weekend work, but so far haven't charged it yet. I've done some weekends but charged my regular rate, but I usually tell clients that I don't work weekends. One actually said "kudos to you" for that attitude and she meant it. We still work together but I don't want to miss my time with my husband and be wiped out on Monday morning. I actually did two seven hour days over a Saturday and Sunday and was wiped on Monday, so I just don't do it anymore.
Nights are a different story. I don't charge extra for that because I take time during the day to do my own stuff - shopping, walking the dog, going to the gym (when I'm being good) so I don't mind working nights. We don't have children and my husband is a much of a workaholic as I am - he's a programmer in a department that is short on staff so he does a lot of work at home in the evening. We don't own a television so we have lots of time on our hands