A couple days ago I got excited about the proposed MetaWeblog API, and then just as quickly became disinterested, because it wasn't trying to solve the problems I thought it was.
However, that night I realized that while it didn't open up the opportunity I was hoping for, it did re-open an opportunity I had given up on long ago. If you recall, a while back I said the Blogger API was not useful to me because it didn't support titles or categories.
I had given up on the Blogger API completely and was looking for a new API whose Lowest Common Denominator was much higher, one that could support the functionality of feature-rich weblogging systems. The idea of grafting a 3rd party API on top of Blogger never occured to me, so when I read the MetaWeblog API's RFC, I was completely confused.
The MetaWeblog API makes it possible for me to use Blogger+MetaWeblog compliant tools to post to my weblog (once MetaWeblog is supported in Conversant, that is). So, it is a good API.
Now that I understand it, I'm excited about it again.
And, I'm also excited about the SuperMetaWeblog API that Hannes has offered to organize, which (I think) aims to address the issues and opportunities that I originally hoped MetaWeblog API would address.