I've found it just fine for whatever clients want to do....EXCEPT....when they need to contact a server over a non-http port. It just can't do that. So for my client who wanted to do apple push notifications for his iPhone app, we needed to use both app-engine and dumb endpoint nodes on rackspace 11 buck a month linux servers.

Amazon Ec2/S3 works well as well and has the highest security bar of all the cloud offerings.

Rackspace is pretty good, but everyone seems very dis-satisfied with the S3 competitor, cloudfiles, so just use them for servers. Don't put anything super valuable there though, they know your root passwords (as does google, if you think about it, on GAE).

The users are on python. Apologies for the poor formatting/spelling, having to rush out the door.