who seems to work well on my installed copy of stable, but you could always just use the $USER variable to show you the current user.

EX:
brenton@trixarian:~$ echo $USER
brenton

The default user of the LiveCD is tux with the user password of tux in case you were wondering :P (The root user is root and the password is root)

What about the command:
#whoami

There's that one too - man, I can't remember commands at 4am hey :P

Funny, who on cooking with the latest upgrades (2.6.37) returns nothing. Although whoami works fine.

Busybox isn't just a light bash. Yes, it has a light shell named ash, but it also includes several common commands and functions, all be it somewhat stripped down versions of them, into a single binary. It's also way smaller.

You might also be correct on the fact that who is broken in that version of busybox though. But just a side note, but bash without it's commands (which are provided seperately and by many binaries) can't do much, if anything. It's only by combining the commands and the shell that you get bash that works like it does. Same with DOS and all it's commands. Without them, it doesn't work every well either.