The lack of automatic updating and regular releases is the real problem with IE as far as I’m concerned. I have to test on multiple versions of IE, whereas I only test on the latest (or near latest) versions of Chrome and FF because I know that most users will be on the latest or upgraded to it shortly.
IE has got a lot better than it used to be, but still misses important features / does things in a strange way. If it can be updated regularly and automatically to keep up with Chrome and FF, that would be a massive improvement on the current situation.