> I know Firefox has switched to an HTML5 parser

Yep, this was mainlined in Firefox 4 (with Gecko 2.0).

> I think IE has made a bunch of noise about it too

Support is being built, it's planned for IE10.

> I don't follow WebKit all that closely, but I'd be surprised if they haven't moved towards an HTML5 parser

The HTML5 parsing algorithm has been in Webkit since the second half of 2010.

And you have not asked, but HTML5 parsing was officially released in Opera 11.6 last month.