Warning: very boring post, but I'm waiting for my computer to finish doing stuff.
My computer started misbehaving in a worrying fashion, so the long overdue backing up became a priority tonight. In the past I've used cdbkup, but various limitations (in particular worries about how easy it would be to actually restore from it) made me switch to KDar, a very nice KDE frontend for dar. I also did lots of cleanup to my directories so backing up is much easier now.
For the first part, directory cleanup and reorganisation, I mainly used bash (my terminal of choice is YaKuake, it docks invisibly to the top of your screen, and shows itself at a keystroke, so it's automatically on every desktop -- very convenient). For getting rid of tons of rubbish I found KDirStat indispensable. Finally, I used k3b to backup to DVD, which worked like a dream (as always for k3b -- it's easily the best designed and implemented CD/DVD burner I've used, and I've tried lots, and it's also beautifully integrated with other apps like Konqueror and Amarok).
My home dir is 26 Gb, but I found I could ignore 75% straight off -- MP3 collection (comes from my CD collection), virtual machines and chroots (I never store important docs in the VM itself, but use things like subversion to keep the important files on my main home dir), downloaded files and some other large but dispensable files.
KDar also supports filtering individual files by pattern matching (as well as including and excluding specific directories), so that can be used to eliminate a lot more.
Finally KDar does compression as well. But it's not as crude as gzipping a taball -- it allows you to choose file types that compression should not be done on (to save time), and it creates archives with a catalog that allows individual files to be retrieved even with just one 'slice' of the archive. So, after all these savings, the archive was down to just 1.8 Gb, and it only took 23 minutes to create. Which was good, because the first time through I forgot to exclude an important directory -- the one that stores my secret GPG key and revocation keys, which I have backed up separately, since I don't want lots of copies of those files hanging around.
KDar supports profiles (a set of options for doing a backup) and also does differential backups, so the next backup should be very little work -- hopefully from now on I'll be more successful at doing them regularly -- once a week is probably about right.