I have my N900 for over 4 years now and I am still happy with it. Two weeks ago my vibrations were dead, I could only hear a slight buzz and no tactile feedback or any shake happened, and yesterday the same.
My fix was entering in x-term
dbus-send --print-reply --system --dest=com.nokia.mce /com/nokia/mce/request com.nokia.mce.request.req_vibrator_pattern_activat e string:'PatternIncomingCall'
and whilst is vibrating just hit it with the back cover on my knee and the vibrations came back.

cheers!