Hi there!
Rosenbagel
-user guide does mention of iButton and RFID support...but that's it. No mention of parts in lists, what reader to get, etc. I see you can get ibuttons fairly cheap (5 for $25ish on amazon), but what kind of reader do you need to interface into the kegboard? Where to get it, etc.
The kegboard firmware supports reading the ibuttons:
http://kegbot.org/docs/kegboard-guide/overview.html#features
You just need a receptacle for it. That'd be this part:
http://www.embeddeddatasystems.com/DS1402D-DR8--Blue-Dot-Receptor-iButton-Reader-Cable-Serial-or-USB_p_88.html
(It is currently backordered, though.)
As to where to get iButtons, I'd stick to resellers such as the one above, or eBay (where you can occasionally find a deal on them.) You can also order all of these parts directly from Maxim, but be forewarned: their commerce system is not designed for consumers. Last time I used it, it was a hassle to log in and complete a transaction. Further more, lead times and shipping costs can be costly.
Rosenbagel
-is ibutton recommended over RFID?
It is in many respects personal preference, what you want out of your kegbot. I prefer the ibuttons for the tactile feel & the unambiguous nature of authenticating (either it is in the socket, or not). There's also the keychain-bling factor
It is also cheaper to build an iButton reader (it is built into Kegboard, as mentioned), since it just requires a spare pin. The cheapest RFID solution would still require some discrete parts, an antenna, etc. That said, Geoff has a really cool looking RFID setup. You can always change your mind, and Kegbot supports multiple authentication sources..
cheers,
mike