Some icons appear twice in the Sidebar I have two MacBooks and a Mac Mini that are synchronized through Mobile Me. All times they synchronize to Mobile Me, the MacBooks (which runs Mac OS X Lion) keep showing some icons two times, in the sidebar of the Finder; this doesn't happen to the Mac Mini, which runs Mac OS X Snow Leopard.

What can I do to avoid this, apart avoiding that the MacBooks running Mac OSX Lion synchronize with Mobile Me?
The reason is because the applications are slightly different for each version of the OS so they are in effect 2 applications. Until you upgrade your mac mini I would recommend turning off syncing of just the dock.