i was wondering if its possible to see every account that has logged onto battle.net from your computer.
i know theres a reg value "lastbnet" that has the last name you logged in as, but is there a place (folder or file)  that every account is stored?

lost mule accounts would be a thing of the past.

i looked in Diablo II/Save but there isnt even account names in there, just some character names.  most of them arent even my characters... like characters i met playing on battlenet. why do these save to MY folder?

You could be able to log the times and names and passwords in a file, BUT Diablo II nor any other Battle.net product does not log them for you.