the UCI minimum weight limit is 15lbs, so most are built to weigh in there or thereabouts - although it's possible to build a bike well under that limit....
It's not just the overall weight that matters, how it's distributed is also significant - if speed is your aim, you want your wheels to be as light as possible, especially the rim and tyre. This, AIUI, is the principle advantage of tubulars - they're much lighter than clinchers.
Bizarrely, Tony Martin has switched from tubulars to clinchers this year and at the Tour de France, suffered punctures twice at crucial times (in the prologue and the second time trial). It will be interesting to see what he uses in tomorrow's Olympic time trial.
Personally, since I don't race, I'm going to save more time by not having to stop to repair punctures than by riding faster, so I use Durano Plus on my road bike - they're pretty heavy compared to racing tyres but on the other hand, my first puncture in the current set came last week after more than 5000km on those tyres.
d.