Disadvantages of RFID

Cost. Bar codes cost less than 1 cent, yet the most optimistic cost for RFID is eventually 5 to 10 cents per tag.
RFID signals may have problems with some materials. Metals and liquids can cause problems reading RFID tags.
RFID does not require line-of-site, but is also restricted by it. An RFID reader will read ALL tags within its range. With a bar code reader, the specific item is scanned and read, allowing you to single-out a specific item.
RFID tags can fail. Although bar code labels can fail also, when reading an entire pallet of product at one time, how do you know if there are damaged RFID tags? How are these exceptions handled?
RFID tags cannot confirm that they were NOT read. This concept is confusing, but we believe it is the most limiting issue when dealing with RFID. Stated differently: in most cases when using RFID technology, you cannot know that you were unable to read a tag. Consider several tagged items within a box passing through an RFID reader. You may read many of the tags, but you typically cannot know that you missed one or more tagged items. Other methods are sometimes employed to attempt to bypass this limitation and attempt to confirm that a tag was missed.

http://ezinearticles.com/?The-Disadvantages-of-RFID-Credit-Cards&id=163596
http://www.usingrfid.com/news/read.asp?lc=s44325nx1433zg
http://www.rossinc.com/aview.aspx?id=13266