The manual that comes with Retrospect is quite well done, and offers in-depth discussions of all of the features provided. The manual works through each main process (backup, archive, restore, and retrieve) so that you can be up and running with basic usage quickly. Then you'll want to go back and peruse the manual more carefully to figure out how to work with the snazzier features like Custom Selectors and unattended backup.
One section that I highly recommend reading is the chapter on Backup strategies. The standard backup strategy that I have my clients use is an alternating disk method, where one disk is always off site. That's not as easy for an individual, but just take it to work or something. None of my clients have ever had to resort to the off-site backup, but then again, none of them have had a fire in their offices yet, which is all it takes to destroy all originals and on-site backups. Retrospect's manual does a good job of talking about various different ways you can achieve the maximum of backup security with the minimum of effort, something I always like since people are inherently lazy about backups.
In case of problems, the manual includes a decent troubleshooting section, although the problems I've had haven't always been discussed in it, and some people complained about not having enough technical information. I did figure out the corrupted Retro.Prep file (see below for details) problem with the help of the troubleshooting section, but it's not always as helpful. At least it does give many, if not all, of the possible error messages and error codes so you can get an idea of what might be going wrong. Do keep in mind that unattended backups bring in more problems and are difficult to troubleshoot. Just recently, a client started having system crashes in the middle of the night randomly, and although this turned out not to be the case, for a while we thought dirty power in the night might have confused the SyQuest drive enough for it to whomp on the SCSI bus and bring down the whole system.
The manual also has a nice reference section that briefly explains all the menu items, the Standard Selectors, the Status Symbols (which indicate if a file is locked or invisible or archived or whatnot), the keyboard shortcuts, and a listing of what's stored in the Retro.Prep file. Then comes a decent glossary, and an index, that, although useful, could have been significantly larger. It took me a minute of searching before I could find the entry on how to deal with AppleShare servers because there wasn't a listing under AppleShare. Instead it was under Network Backup:TOPS & AppleShare, which is a fine place, but not enough in my opinion.