(this is (one of) my favorite blog post titles yet!)
SexyWidget is a smart blog that I have been reading lately. Definitely worth subscribing to - subscribe to Mattishness as well, if you haven't already!
For example, here is a good post about modeling widget distribution.
Here is another good post, this one is a review of local company Shelfari's widget.
One particularly astute observation:
Shelfari is, however, facing a couple of significant challenges. All I have to do to keep my iLike widget loaded with fresh, self-expressive content is to listen to music. Unfortunately, with Shelfari, my completion of a book doesn’t automatically add it to my shelf. I have to log in, search for the book title, and explicitly add it to my shelf. This is a big deal, and there’s really nothing that Shelfari can do about it.