IE7 doesn't support display: block CSS which is quite handy when you have a lot of tables. I'm not sure how well and good it's to make a site without tables and only CSS for layout when it comes to IE.It *is* possible to build pages with no special cases. It gets harder particularly when it comes to IE5 but it is possible. I've had a lot of practise.
IE7 supports a lot more than it's predecessors and the remaining issues were going to overflow to the next version or through fixes although I don't have details beyond the release speech for IE7.
So far as I see it, you're throwing away a lot of good functionality to make it compatible with IE.
And you know how many users like visual effects? Well, IE doesn't support the standard opacity CSS, but FF and Opera does. I'm aware IE has its own effects, but they're not standard and will only work on IE while standards WON'T work on IE. Quite infuriating.