I was using a piece of foam rubber under my Arduino for the Marble Roller project.  Not so nice, right?

Having a brand new MakerBot Replicator 2 on my desk, I decided to, well, make a nice bumper (or 3).

No design time needed as someone else did the hard work: http://www.thingiverse.com/thing:26237

Printed out wonderfully.  Fits perfectly.