[lucisferre]

Depends on a few more things:

1) If it's actually 7% of your revenue as opposed to just global traffic stats.

2) If entrenched IE customers would actually stop using your product rather than just install another browser.

3) If the cost of maintaining shims, backwards compatibility and ultimately just falling behind the competition in both experience and features is less than that potential 7% market.

[markkanof]

And to expand on your points, is there anyone that is an entrenched IE 7 or 8 user because they just love that browser. My guess would be not, and that instead they are just using that because it's the latest version of IE that they can get on their OS. Anecdotally, I've seen a number of large organizations that I work with allow installation of new third party browsers even though they stay at an old version of IE for compatibility reasons.

So my point is that of that 7% that are using older versions of IE, it's probably a much smaller number that would not be willing or able to use an alternate browser to run your web application if they find value in it.