We explicitly don't support IE on our heavy JavaScript web app.

Users get an alert saying, "Use Firefox or Chrome. If you want to use IE and are upset that you can't, let us know."

Nobody has said anything about it.

I think so much depends on your audience. Our audience is writers using their own computer. They're happy to use Firefox and Chrome.

I only see IE6 support as a problem for people on corporate machines who don't control their own software.