Unless you go under the hood with SharePoint 2010, you may not be aware that there is a metatag which forces IE8 compatibility mode. Presumably, this is because SharePoint 2010 and IE9 don’t yet play quite as nicely together as one would expect.
There are issues with:
- The people picker (save button is disabled).
- Web Parts cannot be moved from zone to zone, they go back to their default location when you stop editing the page.
If you want to use CSS3 media queries in SharePoint, you have to remove the IE8 compatibility mode meta tag from the master page (or set it to IE9), but be forewarned, it’s not without issue.
To the best of my knowledge currently, the sad truth is that you can either not have a responsive website and leverage CSS3, or you can but you have to live with a couple of glitches until Microsoft puts out a hotfix which they also presumably will in the not too distant future.
Hope it helps…