I haven't taken the plunge... just waded in. I don't have tubular rims, but wanted to see what they were like. I'm using the clincher S33s. I like the ride. What fogrider said about sealant. They're tough. Corner well. The only downside, IMO, the clincher tubies are heavy.
Tufo has a sponsorship deal with my club, so I bought mine as part of a club order. They were $26 each, sealant was $3.10.
The tufo NA web-site has a discussion group... might be a good place to get some opinions, tho' I bet they'd mostly be kind of biased.
http://www.tufonorthamerica.com/forums/