Sorry if someone else reported the problem already - thought I should share in case noone mentioned this before. As it turns out, Umbraco does not implement .DescendantOrSelf (without "s"!). If you need such functionality, you need to either implement it yourself (see a little patch we created) or go for .DescendantsOrSelf(*).First().

Also see discussion on the subject on our.umbraco.