I have a Thinkpad T410s running Windows 7 64-bit. I have had it for three months. It has the latest BIOS (1.41) and trackpad drivers.
In the last week I have started to notice that the keyboard intermittently stops working.
Specifically, keystrokes have no effect, including Fn-F12 (shutdown) and Ctrl-Alt-Del. The LED on the capslock key does not turn on or off. Whatever state the lighted keys (e.g. mute) were in remains. The trackpad and trackpoint work properly, and I can close apps and properly shut down the machine. When I attach a USB keyboard it is recognized, but no keys work.
If I run the Lenovo keyboard test, all the keys register properly and the caps lock light works again. When I quit the test app, the caps lock light stops working. If I hit Fn-F12 while the keyboard test is running, it goes into hibernation. When the machine comes back from hibernation, once I exit the keyboard test I again cannot do any input on the keyboard.
I'm pretty convinced there is a software or driver problem. I never saw this the first three months I had the laptop. I do not recall installing anything recently. I am sure I've received some Windows security updates. I tried using wired networking instead of wireless - no difference. There doesn't appear to be any inciting event; it usually happens when I am working over ssh. I switched from rxvt+ssh to Putty and the problem still occurs.