That's a nice tutorial and the idea of running Wordpress on GAE is intriguing to say the least.
I apologize that I have not closely familiarized myself with Google Cloud SQL. Is it really API compatible with MySQL, or are there limitation that one is bound to run into when one starts adding plugins etc.?
I also don't quite understand (not having tried it out yet, obviously) how you'll handle static files (images, etc.) uploaded via the Wordpress "media" feature. Is GAE able to support that?
Anyhow, congratulations on the launch. I'm not a huge fan of PHP myself but I frequently find myself having to use it (e.g. to host a Wordpress site!) so this is really an interesting avenue for me to explore.