Graphing statistics over time in Ruby

In my Rails application there are some metrics about the content of the database I made available in an administration interface (number of users, number of users with actual data, rate of usage, numbers of database records in various tables). I can get this information at any point in time, but I wan开发者_如何转开发t to log and graph historical data so I can see trends. I know this problem has been solved a million times before (New Relic and Facebook's Developer Insights being two places I see it daily).

What's the easiest way to approach this in Rails? This is just for my personal curiosity; external services and ugly UIs are okay as long as they're not too difficult to implement.

For the graphing part Google Charts has been pretty useful to me in the past. There's a decent API for it too http://github.com/mattetti/googlecharts