Even though App Engine's features seem nice on paper, and they have relatively decent documentation, I won't use them because I'm afraid that I'll have to contact customer service at some point.

My experience so far with Google is that if something is broken you can post to a newsgroup with the hopes that someone will read it and take action eventually, make enough stink that your story gets to the frontpage of HN or reddit, or know someone with pull at Google.

I'd much rather spend the time up front to build a solution that doesn't require good luck to get support than to gather the ops savings from going with GAE.