It's a nice, clean way to automate your backups. I've been using it for years. Finally switched to removable hard drives as my backup medium when my 5th tape drive died -- DDS3 is so last century.
The key here is "automated". People are lazy, only the most dedicated (or paranoid) will regularly run backups by hand. By automating the system you get to set it up once, then just monitor and tweak it once in a while, swapping media every so often.
Retrospect does well for this.
What's more is that it's cross-platform. I can (and have) backed up Windows, Mac, and Linux clients from the same server. I just wish they'd cut prices a bit on their multi-system licensing. Raising prices sounds like a great way to make more profit, but in the long run it may just lose you customers. And aside from creating CDs and packaging (which is dirt cheap) it's not like the software is a finite resource. Make it cheap enough and hobbyists will buy it in droves, not to mention small businesses.
I was disappointed when I heard that Retrospect 8 was canceled and EMC was talking about dropping it altogether. I'm glad it's still around, and hope that Sonic will do something with it besides let it collect dust.
Anyway, enough babbling! MHO, YMMV.