Checked my notes! It's not 24, it's 20 cars... STILL very impressive, though.
They didn't have multiple copies, but according to the rep, the games have really good multiplayer options (just ad hoc, to my understanding).
In Toca, you get 12 player wireless multiplayer (just ad hoc, to my knowledge) and in Colin you can play pretty much the same stuff wirelessly as you can play multiplayer in the console version.
I'm really looking forward to these two titles, although the racing overload on the PSP is a bit worrying. Then again, Burnout Legends was really good too, so it's better than [nothing].
And off-topic, Virtua Tennis and Lemmings played really well too, so the European launch is sure to have a brilliant line-up.