I am planning to on my trusty GT Timberline. I don't see any major issues, however I have had to buy new forks to fit front racks on. Gone for some Surly Long Haul Trucker forks but not yet fitted them. So still work in progress. I went for a Tubus Logo rear rack as this has good heal clearance.
http://i1165.photobucket.com/albums/q584/jakegil/5e8d8497.jpg
http://i1165.photobucket.com/albums/q584/jakegil/5e8d8497.jpg