I have had (2) die in exactly the same way - feedback starts to get 'softer', then simply stops giving any feedback at all. The touchpad still functions ok, just no clicks or vibrations. The Genius bar has had to send out each time for a "bottom replacement" - took a few days each time. Works for a few months, then dies again.
Such a wonderful machine, but definitely an issue here (with an admittedly very small sample size of me).