Mac OSX Server has GUI based admin tools that will show who is connected and what protocol they are using.
While the server admin tools are interesting, the original question was about Unix tools and "personal file sharing".
To expand on the original question just a bit, when personal file sharing is turned on, is there ANY easy way (or even not so easy way) to see if anyone is currently connected and, if so, who and what protocol (afp over appletalk, afp over tcp/ip, smb, etc.)
Back in the ancient OS9 days you could just go to the file sharing control panel and look.