If you _have_ to support IE, I would just add conditional comments, and make all grid stuff one column and not worry about fancy stuff. IE users just can't expect the internet to pander to an outdated and unsupported browser. If it was supported by MS, I might consider a little more care though.
Unfortunately the website I work on has more users on IE than any other browser. I wish I could use grid but there is just no point when the fallback would be the main way to see the website.
That is a rare circumstance, and I agree with your assessment, no point in making life hard for yourself.
Since IE is no longer supported (or even considered a browser by MS, but a compatibility layer) what kind of site do you work on that is so heavily trafficked by primarily IE?
Its a project management web app. For some reason every IT department seems to have locked all the computers they manage to only running IE, and then they customize the shit out the settings on IE which make the site break in insane ways that we can't test.