same problem here.
started with space key.
now also part of the paint is gone on e r t u i delete a h l n m and .
have to hand it in soon to get it fixed.
i got a replacement phone in beginning of march. after my usb connector broke after 3 weeks use. and i had to fight with nokia for 7 weeks until they fixed it with a replacement phone.
so a little worried to give that crap nokia company my mobile again, 7 weeks to repair is a little long...
i use my keyboard quite a lot. but i also did for years on my previous phone sonyericsson p1i and keys are still fine...