The revisted MetaWeblog API spec is available, with caveats removed, here:

http://www.xmlrpc.com/metaWeblogApi

It's now safe to develop applications based on this spec, however, if
necessary there may be corrections and clarifications to the spec, but no
changes to the underlying format and protocol.

The only change in the format is that there is now a provision for
transmitting appkey's, should applications need to do so.

Thanks to Michael Bernstein for his help editing this document.

Dave