Here in Phoenix, we say YES to slime, at least for off-road riding. I've found that if I park the bike with the valves at the bottom that they don't plug up with the stuff. It is hard to find slime tubes for road bikes here, however, and the LBS guys tell me the roadies don't use them. So this newbie roadie doesn't use slime, and I've learned to watch the road carefully for glass and thorns.