The decision to drop IE should be made after consulting your logs. How many users would you be turning away? If a substantial portion of users are on IE, it may be best to just support IE8 (or maybe only IE9) to ease development problems.
back to ensuring pixel level stylesheet compatibility for IE6-9.
I don't think you have to go that far. I think it's perfectly acceptable to have a fully functioning app that works in most browsers, has a few hacks for IE7+, and a stripped-down version for IE6. Maybe the IE6 version should have nested tables, a high contrast color scheme, and lots of blinking text.