A Vegas stadium would be fucking awesome, but I'm not sure they could have one finished for the 2008 season. The AAA 51s use Cashman Field, and it would never do for major league ball. In fact, the Dodgers nearly dropped their affiliation this year because Cashman doesn't even meet AAA standards. It's not so bad for the fans, but apparently it sucks ass for players. Something about weight machines in the hallways.
Reggie Jackson has been working hard to get a team here, and the two most-mentioned teams are the Fish and the Twins. But what Oscar Goodman really wants is an NBA team (and I think Magic Johnson is leading that effort).
I'm not sure how well the Vegas community would support an MLB team, but as someone else mentioned, you'd get a shitload of visitor traffic.
But as long as Oscar Goodman is mayor, I predict that soon Vegas will get either an MLB or NBA team. Oscar always gets what he wants. Always. And then he has a huge-ass party with titty-girls and Elvis impersonators.
Not that it any of it will matter to me, because we're leaving Vegas as soon as our house sells.