I needed a short and intuitive way of showing dates, so rather than just making something up I decided to steal Google's short date format from Gmail. I'm sure they did usability studies and whatnot.

ActiveSupport::CoreExtensions::Time::Conversions::DATE_FORMATS.merge!(
  :gmail => lambda { |date|
    Time.now.beginning_of_day <= date ?
    "#{date.strftime('%I').to_i}:#{date.strftime('%M')} #{date.strftime('%p').downcase}" :
    Time.now.beginning_of_year <= date ?
    "#{date.strftime('%b')} #{date.day}" :
    "#{date.month}/#{date.day}/#{date.strftime('%y')}"
  }
)

ActiveSupport::CoreExtensions::Date::Conversions::DATE_FORMATS.merge!(
  :gmail => lambda { |date|
    Time.now.beginning_of_day <= date ?
    "#{date.strftime('%I').to_i}:#{date.strftime('%M')} #{date.strftime('%p').downcase}" :
    Time.now.beginning_of_year <= date ?
    "#{date.strftime('%b')} #{date.day}" :
    "#{date.month}/#{date.day}/#{date.strftime('%y')}"
  }
)

Put this code in your "environmen.rb" file in your "RAILS_ROOT/config" directory or make a new Ruby script file containing it in your "RAILS_ROOT/config/initializers" directory.