I thought I remembered reading somewhere that IE9 would not be supporting them, but now after searching I can\'t find any indication that this is true.
Is a
I believe it will have to, otherwise a huge amount of sites will break all at once and it's not in the best Microsoft's interests to make that sort of start for IE9.
If there is going to be some sort of compatibility mode, then it is possible conditional comments will be supported in this mode but not in "pure IE9".
P.S. Just speculations.