Like you, I am the only one who uses mine,
I usually have gkrellm running and I also wondered why I had 2 or 3 users showing.
It was explained to me that it is to do with the various applications running - some of which may be background stuff.
When I tried the "who" command it just said that I was logged in the 2 or 3 times (and not what I was logged into).
when I opened another app or console the number would increase, but when I closed everything, the number DIDN'T, go down, so I am presuming that it showed what I was "into" as well as where I had been (though as yet I don't know what the command is to find the "history"). The only time it would change is when I logged out of the system.
Hope this makes sense!