It works! I can post from YQL
Update: The post above was a test posting from YQL. This is pretty cool! YQL (Yahoo Query Language) lets you do SELECTs from any service on the web. Actually doesn't need to be a service, can be HTML (yes, scraping) or even plain text. Anything is data. If you have a service, you can also create custom tables and expose your data. But now you can not only SELECT, but also INSERT, UPDATE, DELETE (see how).
And checking this post I was just able to create a new WordPress post. This is co cool. It means you can interact with any service by simply using familiar SQL syntax. You don't have to know about XML-RPC and the hassles with WordPress or any other service. You don't need to read every service's (sometimes poor) documentation. It's just tables.