Internet Explorer 9 was mentioned at PDC '09 and I was looking for a download this morning if one exists. Turns out you can't download IE 9 as it is still in development, but there is a blog post here where you can get the IE Development Team's early thoughts on Internet Explorer 9.
Probably more interesting than the blog post are the comments. A lot of people really unhappy about Microsoft continuing to develop Internet Explorer and wondering why they don't just stop developing IE or use WebKit. A lot of people also calling out Microsoft on their downplay of the ACID standards test for web browsers.
Obviously a lot of this frustration is due to the fact that Web UI Development is so painfully hard when you have to test the UI in so many versions of IE that vary in their rendering. UI Developers are tired of testing their browsers in IE 6, 7, and 8, which grossly lag behind in standards, and really don't want to have to now test in an upcoming IE 9.
Some interesting comments that are worth reading on the blog post.
Related Posts: Microsoft Developer Tools and Visual Studio Add-Ins