I've used the vim xmledit plugin for a long time, and for a long time I've had trouble with self-closing tags in xhtml (for instance, br). The plugin would add the trailing "/" automatically, but leave the editing cursor in the wrong place.
This past Friday, I finally took the time to open the plugin and track down the problem. The fix was fairly simple, and I sent a patch to the author for inclusion. He was very enthusiastic and encouraging about my patch. Overall it was a very satisfying experience.
Hurray for me and for open source, but I can't help kicking myself for not doing this years earlier. The idea behind open source is to look at the code and help improve things. Somehow I have to encourage myself to do this kind of thing more.