Currently Post.paginate(:page => 2) returns whole collection (which is confusing), but will_paginate Gem always had the default :per_page setting of 30 (also it validates the parameter to be > 1). I looked at contexts/paging.rb and not sure why it doesn't do something like this:

diff --git a/lib/mongoid/contexts/paging.rb b/lib/mongoid/contexts/paging.rb
index 5bfb844..9f906b1 100644
— a/lib/mongoid/contexts/paging.rb
+++ b/lib/mongoid/contexts/paging.rb
@@ -13,12 +13,8 @@ module Mongoid #:nodoc:

1. A collection of documents paginated.
2. All previous <tt>limit</tt> and <tt>skip</tt> call will be ignored.
   def paginate(pager_options={})

• if pager_options[:per_page]
• options[:limit] = pager_options[:per_page].to_i
• if pager_options[:page]
• options[:skip] = (pager_options[:page].to_i - 1) * pager_options[:per_page].to_i
• end
• end
  + options[:limit] = per_page
  + options[:skip] = (page - 1) * per_page

@collection ||= execute(true)
WillPaginate::Collection.create(page, per_page, count) do |pager|
@@ -43,7 +39,7 @@ module Mongoid #:nodoc:
#

1. The Integer number of documents in each page.
   def per_page

• (options[:limit] || 20).to_i
  + (options[:limit] || 30).to_i
  end
  end
  end