Just wanted to let you know that me and my friends use treehouse quite a bit. We've found it to be a really easy way to share photos with close friends, precisely because of the reasons you wrote about in the article.
Because there isn't any way to restrict the photo viewing to a specific group of friends, I've found that I only add/tell really close friends about it. As a result the quality and quantity of photo sharing goes way up in my network on Treehouse. Compare and contrast this to Facebook where I don't put up pictures at all, and any photo that tags me is zealously filtered to present the best image.
On a side note, some of my friends have complained that the app keeps crashing on iOS4. Anyway good job with Treehouse!