In the off chance that someone on the VS2010 team happens to read this post:
PLEASE PLEASE PLEASE give us a better way of folding (collapsing) XAML. Something like regions would be fine, or some sort of attached property or designer property that we can put on various elements that we want folded when we hit our "collapse to definitions" shortcut. Some stuff I want collapsed, some I don't, please help us out!