I went tubeless early in 2010 and won't go back to tubes. Have not had a flat on the MTB since I converted so it's worth the hassle. On the Stans website, there are videos that show how it's done, so I watched those and converted two wheelsets myself. The only downside, is that the liquid does clump and dry out after some months, turning into dry snot, for lack of a better term. So every 4 months or so (that's been about how long it tends to last out here), I take a few minutes (Really not that long) and unmount the tires, peel off the bigger clumps of snot, and remount and add new liquid. As I have a compressor it's a snap to inflate the tires, but I have had good luck with a quality floor pump as well.
Aside from the obvious, less (or no) flats, the ride quality is much improved. The tires seem to conform to the terrain better, and feel more compliant, less bouncy. I can also run with less pressure in the tires (maybe accounting for the less-bouncy) without fear of pinch flats.
Tzvia- rollin' slow...
Specialized Ruby Expert/mens Bontrager Inform RXL
Specialized SWorks Safire/mens Bontrager Inform RL
Giant Anthem-W XT-XTR/mens Bontrager Inform RXL
Fuji Newest 3 commuter/mens Bontrager Inform RL
Novara E.T.A commuter/mens Bontrager Inform RL