KISSmetrics
We’ve been using Google Analytics to analyse traffic to Citrulu so far, but adding custom events to track significant things (e.g. when a user first creates a real test file) is a massive faff.
We’re currently working on integrating KISSmetrics via its JavaScript API and it looks pretty shiny so far: everything is centered around the user, and you get a load of reporting out of the box by creating your events with standard names. Definitely worth a look if you want to track users progress through a website.