Tubeless tires???

they are tires that have a sealing compound in them, and seal against the complicated rims designed for them. They grip better on terrain since its the wall of the tire being inflated instead of a seperate tube. They dont pinch flat very easily, cause tehre is no tube to pinch, and aparentely they just ride great. I havent seen a tread pattern I like yet so I wont upgrade, even though I have a UST (universal standard for tubless) rear rim on my bike. if anyone knows of a tread pattern very similar to intense system 4 2.25's then let me know

I have been using the Panaracer Trailblaster 1.95 and Mavic tubeless rims for almost this entire season. Worth every penny.
The installation is simpler and the rim(if specific tubeless) doesnt even have a liner. You would however be wise to use a sealant liquid such as slime or Stan's NoTube. One of the big postives for the average rider is the fact that you can add a lot of thicker, more effective sealant in through the bead instead of jamming up the valve stem. I have not had a flat since I started using them, and I had 2 before that and one on my other non-tubless bike.
Traction is superior because the sole of the tire is not made into a "ply". Thus it is able to conform to the surface of the trail better for a given pressure, also increasing ride efficiency and comfort.
Rolling resistance is lowered by a noticable ammount(My mtb commute time dropped by 4mins on 20 miles).
The only thing that fits in the disadvantage category is on-trail fixing. I have a tubeless patch kit, which is simple to use. Patch goes on from the inside. The hard part is inflating it. To get a tubeless tire to "seat" you have to give it a high volume burst of air, whether from a tank/compressor or a CO2 cartridge.
The exeption to that is the recently released Stan's ZTR series rim. It is designed completely different in cross section from a normal rim and is both simpler to instal and can be inflated with a normal pump. Well worth the 95 bucks to get(its also a mere 355g).