I thought you guys may be interested in these 2 articles I wrote. The first is on using the Parallax RFID reader:
In it, I address how to generally use the thing and also how to know when a tag coming in is actually just noise.
I have also written this article on using the ethernet shield:
I go over how to send information that you get on your arduino to servers and I also go over how to design an efficient server side protocol, if that is what you are doing, in Rails.