We've done it before (QoD 07/10/2005 and 04/26/2006, the latter just for poker rooms) and we'll do it again. From the frequency with which we receive this question, we understand that smoky environments are a major issue for many of our readers. If the recent anti-smoking legislation that was passed is enforced, then at least the eating areas of Las Vegas will have cleaner air in the future.
In terms of casinos ever becoming totally smoke-free, however, we've addressed this issue before and remain highly skeptical, due to the significant loss of revenue that's been experienced when casinos both here and elsewhere have tried it. But there is a trend toward Las Vegas becoming somewhat "greener" and in time we may find that larger areas of the casino floors are dedicated to non-smokers. (The new Platinum resort on E. Flamingo is entirely smoke-free, but has no casino.)
For the time being, in many places you still have to request a non-smoking table and will only be granted one if enough fellow gamblers concur; in others where there are dedicated smoke-free zones, you'll often find that they're pretty small and may disappear altogether if the casino becomes extra-busy.
But for what it's worth -- it's interesting to note that out of 97 casinos surveyed, fully 52 have no non-smoking areas, while another 30 have one in the poker room only and some of those are by request -- here's what our latest survey of non-smoking casino areas yielded. We hope it helps.