my old Powerbook was a refurbished model, and it worked flawlessly for 7 years. I strongly recommend an apple refurb model.
Warranty (IIRC) is the same on a refurb model as it is on a new computer, which takes away the fear of buying one. As best I can tell, the only thing that isn't perfect about the refurbs is they lack that "new computer" smell. Other than that, whatever it was brought in for to fix has typically been fixed using new components, so there's really nothing wrong with them other than they're not new in box.
FYI - we retired the Powerbook when the hinge on the screen finally broke (it was a design flaw, really) and we repaired by replacement with a MacBook.