Since IE8 is such a backward browser, I was wondering if there are any web-sites on the Internet that just don't support IE altogether (and block it via conditional comments, for instance)?

I remember stumbling upon web-sites that block Firefox in the past (like ~2004).

The justification of blocking IE is (obviously): You don't want to deal with IE bugs, and you don't want to have to maintain IE-specific hack and workarounds.