Sugru. It's neat stuff and I'm happy with the results, so I sent them a note and picture to their gallery, and reproducing it here.
For some reason I seem to be pretty hard on the plastic "feet" on the bottom of my macbook pro. I've busted three of them
right off and the fourth was looking pretty dodgy.
So, I popped the fourth one off and replaced them with sugru
feet. I used one package of black sugru, divided it into five
equal pieces and reserved one piece for an unrelated repair. The
remaining four pieces I shaped into chubby "coins" the same size
as the original feet. Underneath the feet the case is open to
the inside, and I wanted to be careful not to fill up the guts
of the computer by squishing the Sugru through the holes.
Using pressure around the edges gave a nice convex surface and
ensured a good bond with the case, in addition to keeping the
Sugru on the outside of the case. After it looked like all the
feet were pretty equal, I put a bit of soapy water on a flat
tabletop and set the computer down for a second or two to make
sure everything was level and the unit wouldn't rock. I turned
the computer over to let the Sugru cure.
The Sugru is working much better than the original plastic feet.
In addition to being a lot more sturdy, the grip of the sugru
on a desk or tabletop is excellent.
And as a bonus, my macbook pro got much quieter! I had not realized how
much of a loud hum the disk drive made with the missing foot.
Thanks Sugru, I don't know what else would have worked so well!