post.rb

class Post < ActiveRecord::Base
  
  filter :active, :conditions => { :active => true }
  filter :mine, lambda { |user_id| {:conditions => {:user_id => user_id}} }
  
  sort :date_desc, :order => "date DESC"
  sort :date_asc, :order => "date ASC"
  
end

posts_controller.rb

class PostsController < ApplicationController
  
  def index
   @posts = Post.paginate_filter_and_sort(:page => params[:page], :per_page => 50, :filters => params[:filter], :sort => params[:sort], :filter_params => {:mine => current_user.id})
  end
  
  # vs: (and this doesn't even include multiple filters or sorting)

  def index
    if params[:filter] && params[:filter] == 'mine'
      @posts = Post.mine(current_user.id).paginate(...)
    elsif params[:filter] && params[:filter] == 'active'
      @posts = Post.active.paginate(...)
    else
      @posts = Post.paginate(...)
    end
  end
  
end

# /posts?page=57&filters=active&sort=date_desc
# /posts?page=57&filters=mine,active&sort=date_desc