Re: your Python comment, we already have this ;) http://www.picloud.com/ - I don't usually write comments like this, but I used it about a month ago and was thorougly impressed (no affiliation). Great for stuff where you just want to run a bunch of Python in parallel and not worry about wrangling instances or sysadmin stuff.

When I tried it, jobs up to 40 of their virtual cores (they load share across EC2s) would execute immediately, while more than that triggered job queuing.