This seems very cool. We (www.rjmetrics.com) provide a hosted tool to get metrics like cohort analysis out of the data you've already got on your database. In addition to cohorts, you can also get metrics on time between events, repeat event rates, and segmented lists of lapsed users.

We've got a lot of different visualization options, and we can consolidate multiple data sources (ie Mongo, MySQL, spreadsheets, Google Analytics) into a single reporting portal.