Great questions. Let me answer them one at a time!
Where is the code running? Every script run happens in its own sandbox on our machines. We use docker, it's awesome. People are asking for dedicated machines specifically for their company, and others are asking to hook into their own machines. Once we figure out how people/companies want to use the site, we'll put up some options for where code will be run. I'm totally open to feedback and would love to hear what you think.
I'm measuring costs right now. But I'm seeing that when we get a fair pricing model up - if you could hit these api's only when you need them, rather than have a dedicated server for them, you'd save a money. A really different way of looking at PaaS + Apis... and I'm super excited about it. Right now, I'm just trying to collect as much awesome feedback as possible for use cases, and then we'll have a better idea for how users would want to be charged. Right now, people are asking for a simple request-based model. Would love your thoughts on this as well.
Thanks again for the questions. You're awesome.
paul@blockspring.com 312.834.7265