I suggest often that you should take a break, take some time for yourself. But while I take off a weekend here or there, taking time off is something I don't really do a good job of myself. I really cannot remember the last time I took a full week off from working. I'm thinking it might have been a trip to Denmark in 1999.
As Julie, a blogger for the Chicago Tribune points out, taking some serious time away from work is important to reduce stress and actually be a better employee. Her discussion (here) mentions directives from some companies to their employees on the importance of taking time off.
That is one thing I miss about working in the corporate world: paid vacation. If I take time off, I don't get paid. Further, I don't have anyone to cover my work if I am away. While I love my work arrangement, and I know I wouldn't the flexibility I have now if I worked for someone else, I do wish I could just walk away for a week (or maybe more!).