We had a presentation from Gartner on the use of Biometrics and other security technologies not too long ago. They presented their flashy "Technology Hype Cycle" with a focus on security. Here is an example:

http://watch.state.wi.us/Home/links/...pe%20Cycle.pdf

Here is one of their analyst's comments a bit on fingerprint readers:

http://security1.gartner.com/story.php.id.109.s.1.jsp

I also remember the Gartner presenters stating that humidty and room temperatures changes will affect the fingerprint readers effectiveness. That and any residual jelly on your fingers from jelly-filled doughnuts.