In a little more sinister project, this guy used an AVR micro controller to act as an RFID tag. Hopefully the security gurus see stuff like this in action and realize how bad access control security really can be. The write-up has a few pics and gives a good general overview.
PyroFactor: 
August 20th, 2010 at 6:48 pm
Ah, sorry, this got nothing to do with “security” or “access control”. He is emulating a tag with a static ID, something that is used in product tracking – and not even there any longer, since the simple tags do not offer anti-collision measures.
Someone using static RFID tags for access control can leave the door open…
August 20th, 2010 at 6:55 pm
There’s quite a few systems that use RFID static tags for access control. Check google and you’ll see what I mean. But that doesn’t mean its a good idea.
But I agree with what you said, RFID’s place is for inventory tracking.