Thanks for your rant Bart and I'd largely have to agree.
If you want pixel-perfect equality between all browsers then supporting IE6 is truly a pain. Why anyone would want pixel-perfect equality is beyond me though because the end-users simply don't care.
The real argument for the stuff I've worked on wasn't IE vs. the rest, it was HTML4-ish (IE 6,7,8) vs HTML5 (IE9, FF, Chrome, Safari, Opera). Even then using jQuery + Knockout on the client side solved nearly every compatibility problem.
There was also an actual advantage with testing against older versions of IE as it enabled us to identify weird performance and behavioural problems earlier. When we ignored a given problem in IE6,7,8 during the development phase the same problem would turn up later in all of the other browsers when the system was under load. Fixing the problem for IE6,7,8 got us a massive jump on fixing the problem for all of the other browsers.
Personally for my own stuff the oldest version of IE I test against now is 8. The massive number of XP/IE6 users still out there are in China running a hacked version of XP. As I don't develop for the Chinese market this isn't a problem.