While the auto-opening of rhythmbox every time you plug in your MP3 player is probably great for alot of people, especially if you have a large harddrive player and use it to carry most of your music collection, it’s a pain in the ass when you have a small capacity player and its use is mainly for listening to podcasts.
The pre-hardy heron way was to go to System -> Removable Drives and Media -> Click through the tabs till you see Media player or the like, then change the on-load action to load folder. This made alot of sense, its definately a user preference and most users would think of changing this some where global.
Now in the new, flashy, hardy ways, it has moved to being a nautilus preference, while still leaving many of the other hotplug loading actions in the Removable Drives and Media menu. Why they couldn’t move them all to the same place beats me, but if you’re sick of rhythmbox autoloading you need to load nautilus and go to:
Edit -> Preferences -> Media
Solution from:
http://ubuntuforums.org/showthread.php?t=381041