Here is a pretty neat interactive map that was on USA Today's website that shows airline cutbacks for various states. I don't really know what percent of Las Vegas traffic is US Airways, but it looks like there is a lot of capacity.

On a side note, it's pretty interesting to see how all of the airports stack up. I was suprised to see that DCA has more seats than IAD.

http://www.usatoday.com/travel/news/...cutbacks_n.htm