Ed and I have been busy updating the CSS Sprite Generator to improve it's output quality by using the Imagick library instead of GD and as a result this allows a much tighter control over the output. In the process of doing this we've fixed the large majority of all outstanding bugs with the previous version.
A nice addition to this version is the ability to be able to compress the output (assuming it's png) with the optipng library. This can reduce the image by a significant amount without affecting the output quality so it's well worth investigating.
The branch on launchpad.net will be updated in the next few days and we welcome any bug reports, comments and suggestions on the site.
We're currently considering adding an API interface to the site and would be interested to head anyone's thought on whether they think that would be useful. Clearly for a build script a CLI interface might be something that's higher up on the wishlist and if that's you then please let us know.