It looks like the blogging section of Flock is now working, as I'm sending this from inside Flock! I downloaded the Developers Preview this morning, and so far everything has been really nice.
The delicious integration works pretty well, especially with regards to the search box, which shows options from your favourites and from your history as options. Sweet.
One of the really nice things about the blog editor is the flickr toolbar, which allows you to drag a flickr photo (currently only public ones, though) into a blog entry. No more fiddling with links to add your photos.
Theres a few little niggles, but since this is a preview of a preview, I didn't expect everything to be perfect, but from what I see it's going to be an ace product!