One of the better developments I have enjoyed as of late, is the development of the carbon mountain bike wheel. Reynolds, DT Swiss, Tufo, Fulcrum and EDGE composites have all their own versions of this. And it not just the weight and svelty looks that have me excited - it is more the ride quality.
matched up on KING ISO disc rear hub
My wheels: EDGE Composites has developed a full line of MTB rims, and I have been riding the first generation 32mm profile ones, one set on Chris King ISO hubs and one set on 240s DT hubs. Both are clinchers setup w/ a tubless kit, 28 hole, disc only and the DT's are about 30g lighter - both top out at just over 1300g (1340 vs. 1310). I have also been riding a set of the Reynolds Topo Tubulars which weigh a whopping 1242g, and are gloued up w/ a set of the Dugast Rhino XL's.
DT 240s version w/ CenterLock Shimano discs
If you have ever ridden carbon cyclocross wheels, you know their benefits, they seem to 'float' on rough terrain, and yet are very deliberate in navigation, cutting with surgical-knife precision the direction they are pointed. This is the exact feeling the carbon mtb wheels deliver, without being difficult to handle. Smooth is the word that comes to mind in their overall performance. The buff out the trail in perfect harmony with well tuned suspension and matching tire pressure (25-28psi). These characteristics rand out even louder on my DT's with their stout 15mm though-axel, providing an even more positive, solid front end. I am all for a possible new through axel standard.
The whole package
Tubeless compared to Tubular, they both have strong arguments, however, for day-to-day riding, or in a mountainous/ rocky envionment, tubeless not doubt. The weight is all but forgotten with the added security of flat protection on tubeless, and what I feel is a slightly better performing setup. Go tubular if you have no children to save up for college for, and just need to have that sweet set of 'race only' wheels. Women would also benefit from the superlight weight, so low rolling resistance of tubulars as well.
This is one of the best applications in the bike industry for carbon. Its strengths are glorified and far out shine aluminum or other materials, and its weaknesses are well guarded and hidden. Besides, who can argue with the sheer sexiness of their appearance. Bonus points for psyching out the competition on the starting line with a set of these.