There are a few that do have areas - but not many. Union Plaza has a wifi zone (dont know where it is). But there are other places as well. The one I've used lately is the Krispy Kreme on Fremont. Go in the morning when it is not hot, sit outside and have a coffee and doughnut and surf the web.

McCarran has free wifi as well. Showcase mall has a wifi area, as does a lot of the non-casino hotels (Courtyard, Embassy Suites, Fairfield). Some are free, some are subscription or daily rates.