The Escapist reports that other drivers encountered by the player may be AI, but they may also be other player characters. Ubisoft's press conference revealed that the game has no lobby system, so players can chat, group, join crews, and play through group content in the game world proper. Vehicle customization is apparently a big deal as well, as is the ability to "infiltrate and take over a criminal organization one city at a time."
[Update: Joystiq reports that the title will be coming to PC and next-gen consoles. Click past the cut for a demo video. Thanks to Paul for the official website link!]