I'm running Snow Leopard and I'm sharing my Verizon connection via my Mac's built-in AirPort. Is there any way for me to identify who/what is using my shared connection?
System Preferences » Sharing » Internet Sharing: sharing my Internet access from my Verizon USB Modem (aka Pantech USB Modem) to other computers, through my AirPort card.
I'm sharing my AirPort out to others as an Access Point.
(For Windows, see How can I find out who is using my Windows Internet Connection Sharing (ICS)?)