Hello Tim,
I'd like to contribute a somewhat different (although I suppose common) perspective to this discussion. I help run a free-for-the-community shared webhosting service, and one of the services we have is "automatic installation" of common web applications for people who don't know very much about setting up or deploying applications. Wordpress and MediaWiki are among our most popular installations.
Since it's not reasonable to assume someone who can click a button to setup an application has the know-how to upgrade it manually, any installation that we autoinstall also comes with an upgrade promise: when new versions of the application come out, we reserve the right to automatically upgrade the application for you. (Since we allow users to patch their installs, there are some, ah, technical difficulties associated with this.)
We've noticed several things:
- When Wordpress 3.0 came out, we received several support tickets asking us when we would be pushing an upgrade, and asked us if anything bad would happen if they went ahead and upgraded their install themselves. We have /never/ had this happen for MediaWiki.
- Our spread of versions is quite interesting:
wordpress 649 installs 2.0.2 * 5 + 2.0.4 7 + 2.0.11 4 + 2.1.3 1 + 2.3 2 + 2.3.2 * 1 + 2.3.3 * 29 ++ 2.5.1 * 17 ++ 2.6 1 + 2.6.2 2 + 2.6.3 2 + 2.7 2 + 2.7.1 * 15 + 2.8 * 8 + 2.8.1 1 + 2.8.2 * 2 + 2.8.4 | 6 + 2.8.5 | 3 + 2.9 | 2 + 2.9.1 | 4 + 2.9.2 | 74 +++++ 3.0 | 461 ++++++++++++++++++++++++++++++
mediawiki 1017 installs 1.5.8 * 118 ++++++ 1.11.0 * 125 ++++++ 1.14.0 * 6 + 1.15.0 * 6 + 1.15.1 | 65 +++ 1.15.2 | 15 + 1.15.3 | 18 + 1.15.4 | 664 ++++++++++++++++++++++++++++++
Applications that are on older versions we attempted to upgrade, but had to bail out because there were nontrivial merge conflicts (that is, the user had edited some core files and the upgrade would have obliterated those changes)--there are some exceptions but that is the primary mode by which upgrades failed.
The Star means that we offered installation of that version. Our upgrade process was spotty until about a year and a half ago, when we started really making sure we tracked upstream versions closely.
There are certainly some conclusions to be made here, including "When people patch MediaWiki, they patch it in a way that's really hard to upgrade" and "People don't upgrade MediaWiki by themselves" (note that Wordpress has a spread of versions all over the place, whereas every MediaWiki was from a version we supported."
Let me know if you have any questions; I'd be happy to run other queries on our setup.
Cheers, Edward