The pros have raced on tubular tires pretty much since they were invented. Tire makers like Michelin paid a few teams back in the 1990's to use their clinchers and pretty much every major race in the world was won using them before the payments ended - and the teams went back to tried-and-true, glued on tires.
Why? A tubular rim is almost always lighter than it's clincher counterpart due to not needing any flanges to hold the tire on, just a depression in the center where the tubular mounts, held on with glue. The tires tend to be lighter as well and pinch flats are almost impossible. Perhaps more importantly, a flat tubular is very unlikely to separate from the rim whereas a clincher could come off, making for some nasty consequences. Who would like to see their star rider out for the rest of the season due to a crash caused by a flat tire?
The team mechanics we spoke with back-in-the-day of Michelin clinchers loved 'em. No glue, no mess, no hassles. But the team managers are not the ones gluing 'em on, so the mechanics went back to doing what they were told once the payments ended.
Above: Some of our favorite clincher tires
For the rest of us, tubulars have been sort of a vanity item for years - there's really zero need to mess around with glue and the mounting hassles compared to the ease (and of course the ease of repair) of mounting clincher tires. With the current crop of "open tubular" designs with cotton or other supple casings the ride quality differences are almost zero these days.
NOW, one of the last arguments for tubulars may have finally been destroyed as the rainbow jersey in the elite men's time trial has been won using clincher tires, tires claimed to have LESS rolling resistance than glued-on tubulars. You can read more about this HERE.
We'll concede that if weight is the most important criteria, a carbon-fiber tubular rim with a glued-on tubular tire will still be the lightest setup, but with the hassle of mounting (and the tears when you get a flat) plus less-than-optimum braking performance make this choice rather silly unless all of your rides include a fully-stocked "team car" behind you.
For the rest of us, it's more clear than ever now that the tubular tires' myth of superior rolling resistance has been debunked that an aluminum (Larry would still not ride around the block on a pair of "carbon clincher" wheels) clincher rim with a handmade, supple "open tubular" tire mounted on it is the best combination of ride quality, braking performance, cost-effectiveness and now rolling resistance currently on the market.
For the pros, it'll probably take another round of payments/sponsorships before we see many clinchers back in the pro peloton - but that really shouldn't make much difference to the rest of us.
For more than you probably ever wanted to know about the subject of tires, pressures, widths, etc, click HERE.