Comment 4 for bug 651237

Giovanni,

The problem you encountered with some packages being uninstalled because of dependency specifications is due to the fact that installing the maverick-proposed version of ubuntuone-client using aptitude will require that all of the client packages are specified on the install line, this will get them all at the same version. The alternative would be to do a full upgrade to the maverick-proposed repository, and I don't think that's what you want to do.

so:

sudo aptitude install ubuntuone-client/maverick-proposed ubuntuone-client-gnome/maverick-proposed ubuntuone-client-tools/maverick-proposed libsyncdaemon-1.0-1/maverick-proposed ubuntuone-client/maverick-proposed python-ubuntuone-client/maverick-proposed

should get you where you want to be. You'd also want to add 'ubuntuone-client-dbg' to that if you happen to have the debug extensions installed.