My article, "Building an Ajax Memory Tree" has finally been published on OTN. It was also picked up by Ajaxian today, and got decent reviews there!
In this article, I discuss how you can use ApEx & Ajax to create a new type of Tree. This Ajax-based tree is more lightweight than the built-in ApEx tree. You can also search for a node in my version, and have the Tree automatically expand to that node - something which the built-in ApEx Tree cannot do.
To give credit where credit is due, the basis for the Tree which I create in the article is based on Carl Backstrom's Ajax-based tree.