I had a chance to test a STS-V for the weekend a few weeks back. I am writing my review right now and it should be ready in a week or two.
Bottom line: I like my CTS-V, but the STS-V is a DAMN FAST and DAMN FINE car... Kudos to GM on this one, they got ALOT right! I am a bit jealous of the owners here to have one. A different animal than my V, but certainly fun.
I will post my review here when I finish it (I will have some video too!)!
I was out in Vegas earlier this week, GM set up a small track outside the Sahara Hotel where for $10 ($8 w/ GM Card) and passing a breatholizer you could take two of their cars for a couple of spirited laps around the track along side a professional driver riding shotgun.
STS-V, CTS-V, Corvettes, GTO, SSR, Solstice, etc. Also had an offroad course where you could be impressed by the Hummer H2 / H3 capabilities.
As long as you keep feeding the cashier 10-dollar bills, you could stay out there all day. Most fun I had out there with my pants on...