Yep, this seems to be a very common problem for the w580 phones. My 6 key cracked in half about a month ago, and when I called in to the Rogers support center, the guy knew exactly what I was talking about; said he gets it all the time.
I agree with jacko_oafc: get a rubber keypad. It will also make the phone easier to use, because the standard keys are too slippery
Cheers!