I'm developing a web app so there's some personal frontline experience here. Supporting IE is still a bitch, it sucks badly and it's a punishment. If my target audience were private individuals, I'd say "fuck IE", plug a big "IE not supported" button on the homepage and be done with it. Unfortunately, my target audience is in the corporate environment.
The main problem is that IE does everything differently from everyone else and from version to version. In CSS, for example, sure, other vendors have their prefixes, but writing out half a dozen essentially identical statements for advanced CSS stuff is tedious, but not troublesome. Finding the five different ways the IE wants it done, that are totally incompatible with anything else is just horrible. Google up how IE does CSS gradients vs. how everyone else does it for an example.
For JS, fortunately we have stuff like jQuery or Prototype, and yet plugins to these still list compatability with various browser - and large everyone else is either supported or unsupported and then there's IE. It is very, very, very rare to find a plugin that works on Firefox, but not Chrome, or on Safari, but not Opera. It's a lot more common to find something that works everywhere except IE.
Basically, you can write a web app that runs fine and looks nearly the same on all recent versions of all major browsers, and breaks completely on IE. You would have to consciously try to do the same with any other major browser.