...and see this thread with Stephen White's (GT's tech) super post; http://www.guitartricks.com/forum/showthread.php?t=39932
You can understand my personal quandry and up and down on the issue. Intuitively, I agree with Stephen's guidance and like the idea of at least annual 'check ups.' On the other hand, while there are some season-based changes in the guitars' room, the change in both temp and humidity are small, slow and, I think, minor.
I'll probably take my first two guitars in again at the 12-month point along with my new one. That way I can get a handle on the rate of change, if any change at all, during the past year of those previously set up by my luthier and get the new one its first set-up since coming to its new home.
Until I change my mind/have another idea... ;)
"It takes a lot of devotion and work, or maybe I should say play, because if you love it, that's what it amounts to. I haven't found any shortcuts, and I've been looking for a long time."
-- Chet Atkins