ubun2

Flyback is nice. You can schedule backups and have seperate revisions. It's a clone of Apple's Time Machine. http://code.google.com/p/flyback/
I gave that and others up for simple cron job and a script using rsync. It's not as easy, but you'll learn a lot about the internals of your system. And Cron is nice for scheduling anything.
https://help.ubuntu.com/community/CronHowto
https://help.ubuntu.com/community/rsync
A simple script would look something like this and be in a file called "sombackupfile.sh":
if [ -f /media/back_up_dir/.tagfile ]; thenrsync -avv --log-file=/var/log/back_up_logs/rsync-$(date +%Y-%m-%d).log --exclude=*.iso --exclude=*.avi --exclude=*.mov --exclude=*.mp4 --exclude=*.ogv --exclude=.VirtualBox --ignore-errors --delete-after /home/user_dir/ /media/back_up_dir/elseecho "Tower share not mounted!"exitfi
 
The first line checks to see if it can find ".tagfile" in the /media/back_up_dir directory. If it finds the file, the next line tells the rsync program to move all and keep them in the condition they were in when they were backed up (the -a after rsync). It also tells rsync to show me whats going in a terminal window, if I want to see it (the vv following the -a). The --log-file= option tells rsync where to log what's going on. You can leave it out it you don't want a log. The various --exclude= options tell rsync what not to back up. I don't back up big video files, so I exclude *(any thing).avi *.mp4 etc... I also don't back up the big, hidden .VirtualBox directory, it takes to long. --ignore-errors= will skip files rsync can't read, like files root owns. --delete-after will delete any files from the back up directory that aren't in the directory you're backing up. Finally, /home/user_dir/ is the directory that is being backed up. /media/back_up_directory is the destination.
The last three lines tell the computer to show "Back up drive not mounted!" in the terminal or log. If it can't find .tagfile there, it's not mounted. Then exit the script. That is my probably-could-be-done-better script. No, it's not a quick easy set up, but it's as flexable as you want it to be and I guarantee you'll learn some cool new tricks in the process.