That is... dumb.
Just don't to anything, it'll look broken in IE but no more. If you want to do something specifically about IE, add some kind of warning bar with a conditional comment. You have no idea what the future holds, and locking out a whole line of browsers out of a site is stupid.
On the other hand, if you are a startup trying to gain larger market share, the situation would be of course exact opposite: you will make your service work on as many platforms as possible.
In my case it's a monopoly. People will access the web site because it would be the only official source. Unless my client revolts of course, I'm going to experimentally drop IE support and see what happens.
Don't. What you're doing will be no different from what some of the sites do when they say "You need Internet Explorer" installed.
I'm not a web developer here, so I don't know how much effort will be required but the end result is the same frustration that I encounter when I visit a web page which says "You need Internet Explorer" installed.
I don't consider even IE 8 to be a burden any more. It doesn't get some CSS effects right, but stuff generally renders OK without modification. I can sort of understand blocking IE 8 if you really don't want people to see your site without border-radius or whatever, and if you don't feel like taking the time to patch it up with conditional code, and if all those lost visitors don't matter to you...
But so far I've found IE 9 to be spot-on. Are you experiencing a rendering glitch with the latest beta? If not for rendering issues, then what's to be gained by blocking potential visitors or users just because you don't like their choice of software?
Whenever I've done side projects, I just build it for modern browsers and then maybe make it just a bit better than not working on the most recent IE.