Comment 35 for bug 553655

There is this link posted for what looks like the same issue:

http://speeves.erikin.com/2010/05/ubuntu-lucid-macbook-rhythmbox.html

This person also gets the problem on a Macbook pro, and, surprise, I have a Macbook pro and am experiencing the same issue.

Setting /apps/rhythmbox/plugins/mtpdevice/active = false in gconf-editor fixed the problem for me as well.