Actually, I'm a web developer and I've been looking for a larger site to do a survey exactly like this for a long time.
And as far as changing my behavior developing sites, I'll actually word it a bit differently now -- something like "please upgrade your browser, or if it's out of your control, take a moment to email your manager or IT department to ask them to upgrade your browser, as it is 8 years old and growing."
However, just because users are not empowered to switch away from IE6, that doesn't mean that an IE6 upgrade reminder page is useless. It's just the "squeaky wheel" philosophy of getting things done. If enough users see enough "Upgrade Your Browser!" pages, and if enough of them complain to management often enough, then management might actually do something about it.
Let us not forget that Internet Explorer's market dominance was built on the notion that, after some time, many pages didn't work in other browsers. The only way to break that dominance will involve the same, but in reverse.