Ars Technica just did a browser round-up. IE6 holds < 1% of the United States market now. In Asia, it holds like 40%. Folks kept attributing IE6 to enterprise hold-outs; folks too cheap to upgrade their legacy web apps or get their folks migrated form WinXP / IE6 to something else. But, after staring at the numbers for a bit, IE6 hold-outs seem to stem from pirated versions of Win98 & WinXP. They end up with whatever gets installed, don't upgrade (don't want WGA shutting them down), then they're just sitting out there, legacy apps and security risks, getting viruses, turning into bots for bot-nets, and so forth. IE7 was better, but MS was still of the mind-set that they ruled the internet browser game when it came out. Since then, they've had a rude awakening since Firefox and Chrome have been eating their lunch. Hence, 8 + 9 were more cross-compatible. But, then they shoot themselves in the foot by making 9 Win7+ only. Sure, they want WinXP to die just like IE6, but some folks don't want to pay for a new computer or a new windows license. The comp they have is good enough, and does what they need (web-surfing, email, etc). They're going to stick with WinXP. Of course, those same folks are most likely going to stick with IE, too. But, they'll be stuck on IE8 for the rest of WinXP's life. So, IE8 could turn into the next IE6. Microsoft does this to themselves.
TL;DR, if you're boss is still wondering if your web-app is IE6 compliant, s/he's showing you just how much of an out-of-touch idiot s/he is.