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.