ruby script/plugin install http://svn.tomafro.net/rails/plugins/spraypaint/

Some examples

a) Most tagging queries wrap around the standard finder methods. So the following are all valid:

# Finds with added conditions, limit and offsets

Pub.find :all, :tagged_with_all => ['cosy', 'wood fire', 'real
ale'], :conditions => {:city_id => 'london'}, :limit => 20, :offset =>
10

# Calculations based on tags

Pub.sum :turnover, :tagged_with_any => 'football'

# Finds through associations

City.find_by_name('London').pubs.find(:all, :tagged_with_any =>
['overpriced'])

b) While there is a proper tagging model hidden away, all manipulation is done through strings:
Within your project, generate a migration to create spraypaint specific tables:

  script/generate spraypaint_migration
  rake db:migrate

p = Pub.create :tags => ['dark', 'old men', 'fights']
p.tags << 'wetherspoons'
p.save

p.tag_string = "dark, old men, fights"
p.save

c) There's some rudimentary support for machine tagging:

Film.create :tags => ['film:director:coens']
Film.find :all, :tagged_with_any => {:namespace => :film}
Film.find :all, :tagged_with_any => {:namespace => :film, :predicate
=> :director}

There is currently no advanced documentation for this plugin.