It's up on the Xbox Live Marketplace, not so sure about the PSN at the moment.
It's fucking brilliant.
Graphically, the city you're racing in is really really great looking, and the cars look nice to boot. The game is running at 60FPS, so it's so smooth you could uh... (insert smooth metaphor here). The sound is also really good, with the cars sounding as they should and with a DJ guiding you as to what to do. I played a little bit of online, it seemed solid, there was no apparent lag for me. I didn't try a race however, I'll report back when I do.
The one thing that blew me away however, was the amazing sense of speed. This comes through the framerate, and the motion blur that occurs. It's mind boggling as to how fast you are going. Definitely download this and give it a try.
Crashes look pretty damn good, but the crash cam can get annoying... and it's unskippable. One major flaw I found was the inability to restart races. This means you have to spend a minute or two driving back to the start of the race. This is pretty unacceptable.
Weighs in at 800MB or so.