Hi Dave. I'm going off the statistics that are available to me, comparing the Tcl versions to one another, as Java is immaterial to this discussion. It is a fundamentally different product. (and, of course, when discussing "downloads" one must question whether or not they are actually a good proxy for popularity.)
OpenACS is monolithic; That is, you get _every_ module by downloading just one, huge file.
ACS in contrast is downloaded as a core (1 piece), and as "applications" or "modules". The core, on its own, isn't too useful. People who download it will need to download _other_ modules as well, inflating the download statistics.
Taking a look at the acs-repository, I see that the bboard module (which is the most popular), has 2164 downloads; the "core" has 2714. So, this sounds to me like about 2700 people have downloaded it & given the system a whirl.
On the OpenACS side, I see 1400 downloads of OpenACS 3.2.5 which was released about a 1.5 months ago (!). Which gives me a pretty good sense of how many people are looking. (not to mention the 6700+ downloads of OpenACS 3.2.4, and the 3800 downloads of the RPMS of version 3.2.4)
I therefore conclude that the OpenACS project has a similar -- if not greater following -- than ACS "classic". I don't think I can say how much of that is due to the affiliation with aD corporate versus the inherent utility of openacs, community evangelism + riding on philip's popularity as a "personality". I think the truth is somewhere in the middle.
As a guide, we might look at projects that are achieving similar ends as OpenACS like phpgroupware (http://sourceforge.net/project/showfiles.php?group_id=7305; It's been downloaded in excess of 7,000 times in two months, with no marketing budget, or affiliation with a larger firm. Just word-of-mouth.
An interesting subject, to be sure.
