Vista didn't even exist in final release when this forum started.
There were quite a few Vista forums sprang up towards the closing stages of Vista beta testing. Several have had no more success than this one. I browsed around at the time, having a look at what was on offer. Out of 6 relatively new sites I found, 3 did not make it at all. One has not even had a new post for three months!!
The problem, I believe, is that most users are "Internet aware" and, whilst not being particularly interested in routine visits to forums such as this, they do trawl for help when needed. I could point you to several instances of previous requests for help, where the OP has received help on another forum and is never again seen here.
The reason is simple, and has no easy solution. There are some darned good, long established, sites, with hundreds of very active members, out there. When a trawler arrives with a request, there is usually a flood of almost instant help. The requester gets his result and obviously, does not concern himself with advising on the other (6 ??) forums where he made a similar request.
I don't have a quick remedy for improving the permanent membership. One tongue in cheek idea is to "name drop" when on another forum, but maybe this is a little amoral.
I see a tendency (no offense Mike) towards the problem with Windows 7. The mentioned older sites, have already launched into "7" with separate forums confined to the coming OS. Older members of those sites will probably stay with what they are accustomed to.