I generally don't bother supporting anything lower than IE8. If you want to use my app and are using an old version of IE just download chrome, it's free, otherwise don't use the app. I have used only Linux for about the last five years but i do test in IE using VirtualBox and the free VHD's provided by Microsoft(thanks guys).

I don't mind using the VM approach but the thing that annoys me is the massive size of the VHD files. My Ubuntu install is only about 3GB but each windows VM is around 16GB - 16GB!!! Considering I need a separate VM for every version of IE I want to test and I am using 128GB SSD's in my laptop and Desktop most of my disk space is taken up with having VM's to test IE.

That being said I think it's worth supporting newer versions of IE but I always display a message to users recommending they get a better browser, I think the more people we can get away from using IE the better because while IE10 might be ok now i just don't trust MS ability to update it in the future and i worry that in 10 years we'll all be bitching about IE10 the way we bitch about IE6 now because millions of users will still be running out of date browsers because of the poor update path for IE.