I discovered IDEA back in 2001 when there was no Eclipse and JBuilder was more or less the best choice at the time.
Its truly the best Java editor at the moment (however I would love it to be faster at startup). Well my story is that it had a plugin system from early days and plugin developers started producing add-on features both commerical and free. Over the time these features has also been embrased by JetBrains and included in the standard distribution.
Myself developer a generate toString() plugin that could at the time generate those boiler plate toString() implementations for your domain models that we used to crank in manually. I do think I got a first release of my plugin in late 2002 - can't remember the date exactly.
Over the course of time and new releases of IDEA plugins had breaked due changes in the plugin API. And I must admit that a few times I had started to fall behind and give up on it to refactor and dig into the strange errors why the plugin doesn't work the newer version. And yet again you do have the version issues. How do you support the older version of the plugin at the same time. Yes you can have a CVS/SVN repository and start have branches etc. But at the time most people did only have the source on their local computer and didn't share it in public.
Well the story is that in the next IDEA 8.0 I got an issue reported that my plugin doens't work.
With all these breaking API's during the course of IDEA I do think they have lost quite a few great plugins and plugin developers. Am I the next one? Only time will tell.