To clarify what Harald said: PPA packages aren't signed. If you trust the PPA in question (I'm using the same one for KDE 4.1 packages, and it's on the official announcement, so it should be OK), then go ahead and install them anyway.
To clarify what Harald said: PPA packages aren't signed. If you trust the PPA in question (I'm using the same one for KDE 4.1 packages, and it's on the official announcement, so it should be OK), then go ahead and install them anyway.