Hi Dana,
While Ken Levy may have a rather biased view :) my experience with VFP 9 has been a total pleasure. I've run into no major problems porting apps from VFP 6, 7, and 8 to VFP 9. VFP 9 is an extremely solid product. Personally I think VFP 9 is the most solid product in Microsoft's entire product line.
Jim mentioned some 2065 errors. These can be worked around with sys(1104) calls. Search the UT archives for details.
I haven't come across any other show stoppers.
Good luck moving to VFP 9 - I think you and your contractor will enjoy the experience.
Malcolm