There's the obvious HTML5 hitlist, in no particular order:

- Offline appcache
- Canvas
- Workers
- Sockets
- Web forms

Also:

- JavaScript support - what level should we expect, i.e. .forEach going to make an appearance? (or is in that in IE8?)
- HTMLElement objects - would be great to extend these, IE9 doesn't currently expose these objects (or prev1 didn't).

I'd love to see a gauge of each of those and whether they're on the radar and possibly how far away.  

I think equally as important is the release cycle schedule.  They've done well to keep to their promise of two months in and we've got IE9prev2 - are the rest on track?  Do they have an eye on IE10, 11, etc?  Will we see yearly releases, etc?  These are important factors that help us push the upgrade from "older browsers" to the newer, more secure browsers.

I absolutely respect their efforts so far in IE9, and the SVG support is very exciting, particularly with libraries like Raphäel out there.  You asked, so I'm asking ;-)