Is any of the other major photosharing sites better than Flickr for the albums hierarchy? I mean the possibility to define a depth of more than two... If I'm not mistaken in flickr you can only define Collections and then Albums in those Collections, but you can't get any deeper.
Flickr does allow a collection to contain either sets, or other collections, giving you that hierarchy
SmugMug allows for what is essentially three levels:
Categories --Subcategories ----Galleries
You can completely customize the names of Categories, Subcategories, and Galleries.