Well i've hit my first (show stopper) snag with Beta 2 of Whidbey. It seems using a ATL Com component and the Open/SaveFileDialog() with the Beta 2 release has a problem with the ShowDialog() method. If hte parent window has an ATL COM component (in my case the excellent DockStudioXP control) and you call the ShowDialog() method, as soon as the dialog is closed the control looses the subclassing and renders the control unusable. Pretty major bug (although it serves me right for using COM Interop)...
I reported this to Innovasys and Paul Wilde has already posted a report on BFC about this and a couple of days ago MS have reported it to be "reproducable"... now its time to wait for a fix:-(
The plan of having HotHTML 4 early preview releases to some folks may change now that this issue has come into light, theres always rolling out a temporary "lame" solution - what i've been doing is making the parent an empty temporary form while the dialog is shown, and unloading it after its closed... it works great internally but its not a very professional workaround;-)