I've just discovered Google Browser Sync. This excellent Firefox extension enables you to synchronise browser settings such as bookmarks, persistent cookies and (most importantly of all) saved passwords between instances of Firefox on different machines.
For me, this really is a boon because I like to keep updating to the most recent version of Kubuntu as soon as it comes out, and I have in the past always done a fresh install each time, as I find that is the best way to upgrade. It is a real pain having to update all the passwords for all the sites I use every time.
But I think next time I install Kubuntu I'm going to set up my home directory on a separate partition so this shouldn't arise again anyway! Still, I've used Google Bookmarks for ages now and I find it really useful to be able to synchronise my bookmarks between different machines, so I imagine Google Browser Sync will be similarly useful.