Actually, the first issue I have is that it's called a weblog API....it's a CMS API, or maybe just a publish-editing API. We're stuck in this concept of "blog". With structured blogging (yep, that damn word again...but I guess that's what you get when all you have is one big text blob to shove data structures into*) just on the horizon, tools like ecto, Qumana, and MarsEdit are going to be pushed to work with the myriad number of web apps out there, and the different ways they've implemented some of the loose aspects of these APIs. Actually, this post was inspired by Gus Mueller's post on the MarsEdit 1.1 beta, where he mentions "the sorry state of weblog api implementations right now, and yes- that even includes you atom."
So...what to do? Well, this is one of the things that needs work both on the web app side and the client side. On the web application side, I'm hoping we'll have a special interest group focused on this at the Open Source CMS and Blogging Tools Summit here in Vancouver right before Northern Voice and MooseCamp.
*Why the rant about blogging and "big text blobs"? Well, I'm biased by my tool of choice, Drupal. We've got separate content types for structured information, like events or reviews, and so don't need to take a step back and find ways to mark up structured information inside text. Of course, we'll support structured blogging standards and formats as they arise (and yes, those funky XHTML level microformats, too). Canter's Law, and all that.
My final comment: in all of these things we develop, we have to think less about talking to single point aggregators and namespaces (e.g. Technorati for tags), and think more about every single website as producer and consumer. Aggregation everywhere, and a rich mesh directly between my site and your site, between me and you, not intermediated by several large players.
Heck, if those large players want to come along and crawl my standard RSS 2.0 categories, they can win by giving us kick ass interfaces and great tools for slicing and dicing. But I'm not going to work with your made up formats, I'm going to work towards global standards that work for everyone.