Very useful plugin that formats timestamps to human-friendly relative dates.
<%= relative_time(Time.now) %> # today <%= relative_time(1.day.ago) %> # yesterday <%= relative_time(1.day.from_now) %> # tomorrow <%= relative_time_span([Time.now, 5.days.from_now]) %> # May 17th - 22nd
To install:
script/plugin install http://ar-code.svn.engineyard.com/plugins/relativetimehelpers