title: acts_as_taggable_on find existing tags to suggest from content
body: <p>We're using the (brilliant) acts_as_taggable_on Rails gem, allowing users to add tags to content they write (e.g. blog comment).  We auto-suggest on as they type, but would also like to identify tags that we can suggest based on the user's content.</p>
  
  <p>So if the user typed "We really loved the aquarium in Boston" and we had existing tags for "boston" and "aquarium" we might suggest those.</p>
  
  <p>I think this is simple conceptually (iterate words, check the tags list, order by frequency of use), but there are little nuances, performance implications, and well, you know -- always harder than it looks.</p>
  
  <p>Any suggestions for existing code or examples that might help me avoid recreating a wheel?</p>
  
  <p>Thanks!</p>