The multiplayer lobby in the recent versions doesn't work very well in practice. Last time I tried it, both players always had the same car even if the joining player tried to choose a different one. Also, it's hard enough to keep the cars and tracks synchronized between friends. I imagine random people joining the lobby would have trouble getting a game going with anything other than Carlswood and Murcielago combination.
The host/join with IP address in old Racer versions buggy in some ways, but usually it worked well enough to be fun.