I've been trying to make my URLs even more search engine friendly lately. I've gotten away from using integer values in the URL for anything except the admin/non-public side of my applications. I've been using a :base_name column combined that with some routing.
In the model I do:
before_save :base_name_from_title
def base_name_from_title self.base_name = title.downcase.gsub( /\ and\ /, '-' ). gsub( /\ on\ /, '-' ). gsub( /[^a-zA-Z0-9\-]/, '-' ). gsub( /[\-]+/, '-' ). gsub( /[\-]$/, '' ). gsub( /^[\-]/, '' ) end
"title" is whatever important wordy field I can pick out of a given model. It's tough to pick sometimes especially if the field isn't unique. I don't have too many collisions on my personal blog though.
Then I add a route:
map.connect "category/:base_name", :controller => 'category', :action => 'index', :requirements => { :base_name => /[\w-]+/ }, :base_name => nil
Then in the controller I look it up by base_name instead of by id:
Category.find( :first, :conditions => [ 'base_name = ?', params[:base_name] ] )
Don't forget to index that text field! 
Then my URLs look like: