I actually ended up taking two weeks off total. I could have and somewhat wanted to go back before that, but I wanted to make sure that I was fully able to do my job when I got back. Since my job (at that point) was alot of lifting and moving PCs around, I decided to go ahead and take the rest of the week off.
But more than anything, make sure that you have ample time. If you got 3 weeks you can schedule off and not endanger your job, plan on that much. If you don't need it, great, but it's better to plan for the worst and be elated for the best =)