Ok, I’ve been keeping an eye on this, and with the recent preview 6, there are still some big missing pieces in their CSS3 support:
- CSS3 gradients
- Flexible box model
- Text shadow
if (document.body.style.msTransform !== 'undefined') alert("IE9!");
In short, it seems to have relative parity with Opera 10 as far as cool-yet-useful CSS3 features. Keep going, Microsoft, I’m totally cheering for you!