It's a node.js app that has until recently been a single-process app. I just integrated clustering to take advantage of the extra cores Linode gave me. It's a simple but high traffic service and node has handled it like a champ. I have a relatively inexpensive account with Linode that so far has suited the site's traffic just fine.

I'm exploring the idea of offering a higher-tier service. The general feature list is outlined on getjsonip.com but pricing isn't finalized. I'm still collecting signups and feedback right now.