I've just finished my 11 hours long Saturday working day. In general it's an exception that I work at a weekend but from time to time there is a need and I don't mind but nothing again comes for free. My brain is burnt and it was really hard to be innovative today which perfectly fits into the first paragraph of Roy's post. Needless to say that the rest of the post is valuable as well.
I know people that work long hours for months and they still claim they are productive. Maybe there is something wrong with me but I do believe that everyone needs to find time to recharge its batteries. And it doesn't matter whether you like/hate/love your job.