According to popcon I have just under 1000 users of xen-tools.
That was quite a suprise to discover via a random google search, although I guess there have been a lot of bugs filed against the package during its lifetime.
Funny how some things which start as random hacks (this was originally a quick and dirty hack for a Xen introduction article) become quite useful/popular, whereas other tools which were planned and designed go virtually unnoticed...