I more or less did this last year. I didn't say "no" to everything, but I basically stopped looking for new work by May. I then worked a max of a couple hours a day for the rest of the year.

Starting in November and December I started looking for stuff again-- I picked up a number of great clients for the new year, and it worked out quite well.

This plan obviously works a bit better if you have a few months savings to cushion any unforeseen droughts.