You might want to check if you have the kdar package available. It is a kde front end to dar. You can set up your backup graphically. You can run the full backup or incremental backup graphically, or export a script which could run as a cron job.

For backing up files in your Documents directory, there would be nothing wrong with using tar. Look in the info manual and search for "incremental dumps". (Section 5.2)
Using the "--listed-incremental-file" option you can easily backup up only the documents that have been changed.

You could also simply copy your documents as well to the external drive.

If you are doing LAMP, you've got to check out Zmanda Recovery Manager for MySQL. It will pretty much take care of everything for MySQL, including incrementals: http://www.zmanda.com/backup-mysql.html (note that the "community" edition is free and open source.)

I have a theory about this. Developing good backup software takes a huge amount of effort, and it has to be rock solid, because you have to trust it. Developing and integrating a good GUI is also a huge amount of effort (especially if it has to support multiple platforms). A commercial software company can hire several programmers and assign them parts of it. An open source project tends to be centered around one programmer with a handful of others contributing. If it takes off and becomes a significant stable product, then it might have a few more decent programmers involved. But it is very unlikely to achieve the same energy, quality and time contributed to a GUI. I mean, if you are a top notch programmer, where's the glory in putting a GUI on someone else's backup program?

The one full GUI backup program that I ever unequivocally endorsed was Retrospect (a commercial product originally from Dantz Development); and, since it was bought out by EMC a few years back, it has gradually fallen to neglect and hasn't kept up with changes in the operating systems that people are using. Current versions have too many problems and the support is just plain poor. In the mid 1990's, their support was so awesome that once I posted a message to the independent user's list and half an hour later someone from Dantz tech support called me on the telephone to help me out (it was an issue with drivers for a particular tape drive).

So even in the commercial arena, cost cutting and efforts to get a profit out of a product can result in inadequate programming support to maintain the backup functionality and the GUI.

Anyway, that's my theory. And I am familiar with the open source and commercial backup products out there.

It's Kbackup, which is really straightforward, almost too much so. I'm still not sure if I'm missing any settings somewhere. I don't want to have to re-customize everything, including the look of the clock or the background settings.

Where would that stuff be, or better yet, can someone point me to a book or a website that has entries for all the main Linux folders and what all is in them?