Occasionally Drupal.org has a survey on the use of PHP and databases. The information could be put into the user's profile in Drupal.org so you always have an exact representation of the current usage. Let people tick the releases of Drupal, PHP, MySQL, PostgreSQL, and Oracle they currently use. You then have the information continuously available and can plot the trend.
It might make it easier to find answers if all the support wasn't clumped into one topic. It has 28,000 posts ... wow.
What about
Intall
Theming
Modules
Multisite
Just a suggestion.
I'd prefer to dig around and find answers on my own, but it's all scattered around in little shreds here and there. Maybe it's better just to ask. Maybe the ideal would be some obsessive/compulsive technical writer type to compile info into how-to's.
I think that api.drupal.org should have the current stable Drupal release at the top of the list in the side menu, and also as the default search box. It's what most people are going to be looking for, and could avoid some confusion if people end up searching the HEAD documentation by mistake.
I did a search for the phrase "Using CVS" (without the quotes) and got the following message that I couldn't understand: You must include at least one positive keyword with 3 characters or more.