Diaries are for the poster. You can post whatever you'd like, and they are nice for informal conversation. They also allow you to keep track of and organize thoughts for later.
However, these have got to be one of the most unfriendly formats for finding relevant information that I have come across in some time. Entries are not titled, indexed in any way, rated, or anything. It is just 2234509850907834 random posts to read through in a big pile. For now, Advogato is small, so the pile is almost of a managable size for those with too much spare time on their hands to sift through it all looking for the good stuff. But that trend won't continue for much longer. Besides, even now it is too much for the casual user to go read through all the diary entries looking for something good. In fact, I'd be suprised if more than a handful of people read this entry. Searching, indexing, and bidirectional annotations are desperately needed here.