Earlier this summer, several people were asking for tallies on this. This article claims he's been at the "ranch" in Crawford, or en route there, for 166 days so far since he took office -- this is his 26th trip. Out of 949 days, that's about 17.5% of the time.
http://www.usatoday.com/news/washington/2003-08-24-bush-vacation_x.htmIt doesn't count weekends or other days spent at Camp David, Kennebunkport, or his brother's place in Florida. Or down time while on overseas trips.
CBS estimated total vacation days (as of the beginning of this month) at around 250.
http://www.dailykos.com/archives/003649.htmlComparison to other presidents, including his dad:
http://www.geocities.com/jmoore1350/Column0065.html