I know vs2008 express didn't. I'm hoping this will change with vs2010. Anyone know? Link me?
Edit:
Anyone have a primary source? While "As far as I know" answers can be helpful, in this case it still leaves a possibility - which is exactly where I started.
I don't know, but I would guess that it would not. Microsoft wants to make money, and supporting ad-ins is one of the biggest reasons to pony up the dough for the standard edition. Ad-in support alone can replace a lot of the stuff that you pay for, like SVN and other source control integration, test framework integration, resharper, etc.
As far as I know, the policy regarding Add-In's and Express editions has not changed.