Tracking value changes in ActiveRecord objects

Info about getting to old / new values on activerecord objects:

http://ryandaigle.com/articles/2008/3/31/what-s-new-in-edge-rails-dirty-objects

This can be useful if validation varies based upon the prior state of the the object, etc.

Rails Time Zone Support

A good summary of how to support users in different time zones:

http://mad.ly/2008/04/09/rails-21-time-zone-support-an-overview/