I have one alt (created a few days ago), but he looks just like my main av, and my closer
SL friends already know about him. I made him mainly for backup, testing, and group creation, and the occasional going incognito.
As for having me and an alt online at the same time, I've never done that in
SL, since the viewer tells me I can't open it more than once at a time. (I've done it in
There, though, since you can run multiple instances of the There client on one computer. My alt and I even played in a "Double Trouble" spades tournament once, in which players partnered themselves using an alt.)