Just deleted about 3 gigs of files uploaded to csssprites.com because I'm running out of disk space. I keep the .html results though, just for stats purposes. So
ls | wc -l says that there are 3170 files meaning over 3000 sprite images were produced already, nice.
The tool is very primitive, I admit, its main purpose was to raise awareness of the CSS sprites technique. It's missing a lot of features (as any weekend project do), but I'd say it allows developers to start quickly with the sprites and to admire faster loading web sites in less seconds than it takes to say "OK, how I have open Photoshop and to create one big image of all my smaller images and write down the coordinates in a css file".