I had an annoying thing happen earlier this week.  I was looking at DotNetNuke for a potential project and used their VSI package which allows you to create new sites from within Visual Studios New WebSite wizard. 

Due to an incompatibility I wanted to go from version 4.2 to 4.0, there was no un-install functionality for the VSI package and installing 4.0 over the top of 4.2 made visual studio just freeze trying to bring up the new web project dialog.

After a bit of googling I found Microsoft have a power toys kit for VSI, it allows listing of all installed VSI packages with the option to un-install them, it also gives you lots of help to create your own package, something I haven't looked at yet but at least I know it's there if I need it.

So if you want to trim down some of the packages you've installed I'd highly recommend getting this tool (just look on microsoft/msdn downloads, I'm sure the link will change if I put it here).