While I don't have much experience with the Thinkpad fingerprint readers, I have used them on HP laptops and I suspect that from a hardware point of view they're very similar.
They do get gunked up with dirt over time so for accuracy it's important to keep them clean.
They do sometimes fail to recognize the finger, requiring a 2nd swipe, and generally this is due to not swiping enough of the fingerprint or possibly being off-center. I find if I look while swiping I get nearly 100%.
I originally thought the readers were gimmicks too but what turned me on to them was that, depending on the software, you can use the reader for web site authentication, Outlook logon, etc. If it was just for the daily Windows logon I wouldn't be as interested.
Regards
Wouldn't it also be interesting to know whether it's secure? Will it correctly fail to recognize other people's fingers? – innaM – 2009-09-16T06:33:03.823
It is not really secure as any other fingerprint reader. They will happily accept a printed on paper version of your fingerprint. – vava – 2009-09-16T10:36:36.517
2By the way, I would suggest to roll in more than one finger. First of all it is sometimes convenient use other hand to authenticate, and then it saves you from trouble when you cut your finger and forgot a password. – vava – 2009-09-16T10:39:09.240