You should be starting to get an idea of Retrospect's power by now. The next few items make up the core of Retrospect's power. The most powerful feature Retrospect has, in my opinion, is the ability to create custom Selectors. As an example of how I use custom Selectors, consider my hard disk. I own a number of disk recovery packages, all of which like to create invisible files on my hard disk to keep track of what files I have deleted and other hard disk technicalities. Those files can get quite large and there's absolutely no reason why you would want to store them in your backup set. An organization I know that uses Retrospect also uses TOPS, which has a nasty habit of creating Desktop files in any folder that is mounted as a volume, thus littering the hard disks with tons of invisible Desktop files. Originally, we created a custom Selector that looked for files called Desktop and specifically avoided them. Then we realized that those files, like all the disk recovery files on my hard disk, are invisible, so we switched to using a Selector that avoided all invisible files. Similarly, I had the custom Selector set to make Retrospect not compress already compressed files by searching for the creator codes of those applications.
There are two levels to custom Selectors. First, you choose the items, or conditions, and the relationship between them, And, Or, or None, each of which do precisely what the logic says they should. Second, within each individual condition, you can choose whether it affects files directly, or if its negation should affect them (i.e., either select all invisible files, or don't select invisible files). You can also enable and disable an individual condition for testing purposes. You can choose generic conditions and modify them as you wish, or you can select a pre-existing Selector and include that as a condition. I've found that the nesting power extremely helpful on occasion. As far as the generic conditions go, you can select files based on date ranges, file kind, file flags (Marked, Archive Flag, File Busy, Locked, Invisible, Alias, Name Locked, Stationery, or Custom Icon - remember that Retrospect 1.3 is System 7-compatible, which accounts for the last four flags), folders (and you can select whether files in that folder only or all files and folders below it in the hierarchy should be affected), icon color, name (I love using this one to avoid backing up huge dictionaries), privileges, and Size. Needless to say, if there is a pattern to the files you want to include or exclude, you should be able to define a custom Selector that will do what you want.
The next most useful feature I use in Retrospect is its ability to operate unattended. Like everyone else, I don't like having to back up all the time. However, if you are willing to leave your Mac on a fair amount of the time and have a removable cartridge drive or tape drive, Retrospect can work entirely on its own after a little setup. Since Retrospect remembers what you do at each step and stores that information in a script, all you have to do to start an unattended backup system is run through what you want once, then pull up the Calendar from the Config menu. It looks like a calendar for the current month, and you can double-click in any day to have Retrospect start up every month on that day. You can also double-click on the days of the week at the top of the calendar to have Retrospect work on every Monday, say. Finally, you can set a Run Once date so you'll have a backup done as of that day. You must set several options for all of this to happen though. First, there's the Install Startup INIT checkbox which will install an INIT that launches Retrospect at the appropriate time. All the other options require that INIT to work. Then there's an Auto Launch feature which actually does the launching, a Notification Icons option that notifies you if you're working on the Mac when Retrospect wants to start up, and finally, a Shutdown Alerts checkbox which warns you that Retrospect wants to back up later on if you try to shut down the Mac.
Retrospect allows you to create different scripts which do different things, and you can assign different calendar options to those different scripts. I've had trouble with this in practice, because I find that people tend to modify scripts unknowingly, which can produce unexpected results.
The final important feature in Retrospect does not provide more functionality but does make selecting files easier. The Browser window in which you select files can be customized to your liking. You can pick how each entry looks and what information (such as creator and type and privileges) shows. You can also specify what items are listed and how they are listed (flat-file or hierarchical), as well as the sorting order (normal or reverse) by name, date, size, kind, or color. Sick as it may seem, I find that I end up doing a certain amount of disk management in Retrospect since its provides a lot of information that isn't available in the Finder or in DiskTop, the main Finder replacement I use. You can't move or rename files within Retrospect, but you can delete them, and I find myself using that feature quite often when I'm in the middle of disk cleaning (which happens whenever I run out of room).