I have a similar problem with 3000 Y200 (6469 22R); some of the keys have stopped working without any hints of physical damage. The affected keys are space, x, g and left alt, seriously damaging the writing speed. Sometimes the keys are inactive for a very long time while other keys are working properly, sometimes the problematic keys work like other keys for some time.
The problem persists both in Windows Vista and Linux so the roots of the problem seem to go down to BIOS or hardware level. (With Linux it became apparent that the ACPI BIOS in this machine is broken, too, giving CPU frequency alternatives of 600/800Mhz only instead of the processor's eight steps all the way up to 1.33Ghz).