Definitely insurmountable in the environment of many of our users. They're doctors working with medical data, so IT has to certify anything new installed.

So they're stuck with IE6, because that was the latest & greatest when large custom web-based applications really took off, so they're all certified for IE6 only and would have to be replaced at enormous cost before the users can be allowed to upgrade (or install chromeframe, for example).

It's a big barrier.