The heavy lifting is done in C# as well, on a pile of EC2 machines that gets spun up each night. Back before EC2 Windows instances came out, it was running under Mono, with the help of a bunch of Ruby scripts to handle everything that Mono let me down on (such as ALL the downloading, uploading, talking to webservices, etc. that require pieces of .NET that is hard to implement and non-sexy and thus didn't get implemented by the Mono team).

Now it's all C#, leveraging a half dozen Amazon Web Services and running on EC2 Windows instances.