I have not been online all the much but the few times that I did...I hated and enjoyed it. I still don't know how to get out of the everyday cars but that is b/c I have not taken the time to figure it out.
If your get into it, the online play is amazingly fun. There are heaps of challenges and stuff. THERE ARE NO BORING LOBBYS. That is the best part. You're always driving. Your SP from singleplayer carries over to Multiplayer, but your cars don't. You unlock them differently in Multiplayer. And you get upgrades for miltstones, instead of doing special races. You might of not been able to change out of your Everyday car because that was the car type for that challenge/race at the time. It changes. Read the manual about it though. You learn lots. :P