I've used it, too. I've seen torrents for both XP Black and BlackXP. Judging by the programs packaged with them (for CD versions) they're either from different packagers or just reflect a major change between releases.
BlackXP - Uses Windowblinds for the Vista Aeroglass theme and comes packaged with tons of programs. They make both a CD and DVD release. It's also a cracked version of XP.
XP Black - Is an OEM/Student liscense of XP, so there are NO cracks applied other than the unattended install and slipstreamed programs. It uses nextstep (optional) for a slick, vista-esque theme with sidebar and quicklaunch tools. Without that program, though, it still has some pretty nice system themes that change the layout very well without using any extra system resources (which is nice because NextStep is a memory hog).
Both systems are fine with Windows update and pass Windows Genuine test.
If you're using an older computer and you either A) don't need the extra software B) Don't care if your system looks like Vista or not or C) Prefer to use open licenses over hacked programs, then you should probably choose XP Black. Also, it seems to run a bit better on older systems (once you remove NextStep from the boot processes.)