This is sparked by a comment in the recent "'regexp' and 'useful' plugins available" post, and details a pet peeve of mine re: IDEA.
Keep in mind that I've never looked at the plugin API, nor have I rooted around in the plugin jar files, so everything I write here is from the point of view of a user, not a plugin developer. Some of this stuff may already be available in Aurora (which I don't use),and some it may be available in Ariadne -- I'm more than willing to be told I'm an idiot, in other words.
I'm constantly surprised by the state of IDEA's plugin management, both at www.intellij.org and in the app itself, especially when it's already been done so well by other projects.
For a good example of a plugin manager that works, and works well, see jEdit (http://www.jedit.org). The big (non-API-related) plugin items I see missing in IDEA at the moment are:
1) the ability to install, update, and remove plugins from within the application; the list of plugins should show the complete set of potential plugins and mark those that are installed
2) the ability to get simple, human-readable plugin descriptions while installing
3) the ability for plugins to have dependencies, which are automatically marked and installed when necessaryjn
4) the ability for plugins to include easily-reachable help documentation that lives in a submenu of the 'Help' menu
5) a central, consistently updated repository of plugin information on the web, which serves to duplicate the information available from the in-program plugin manager. all the information available in one should be available in the other.
I know I'm missing things here -- jEdit's plugin management is really well done -- but that's the gist of it.
I see two ways to approach "fixing" something like this, assuming people see this as an area that needs fixing.
The first would be by creating a community-run plugin management plugin and an associated website that provided all the right information and download access to the plugins. You could, in fact, provide all the functionality listed above without any explicit help from IDEA.
The other way, and arguably the 'correct' way, is for IDEA to have a built-in plugin manager; that's the only way I envision something like this becoming really useful, since it's the only way to ensure that plugin authors actually provide things like descriptions and help files and dependency information.
Anyway. I'm just rambling, and thinking fondly of one of the only things I really miss from jEdit.