Rails 2.0 Gotchas

The deprecation tools for Rails 2.0 are grand, but they really don't tell you everything you need to know. The things that have bitten me so far are:

• The built-in pagination has been removed from the core framework. Unlike tools like acts_as_list and acts_as_tree, however, there's no obvious plugin that makes the old code work. This is because the old pagination code was really awful: it performed poorly and hid your content from search engines. Fortunately, Sara was able to convert my paginate calls to use the will_paginate plugin pretty easily.
• Rails Engines, or at least the restful_comments plugin built on top of them, don't seem to work at all. So I've had to disable the comments and proofreading request system I spent November through January building.
• Rails 2.0 adds some spiffy automated code to prevent cross-site-scripting security holes. For some reason this breaks my cross-controller AJAX calls, so I've had to add

  protect_from_forgery :except => [my old actions]

  to those controllers after getting InvalidAuthenticityToken exceptions.
• The default session has been changed from a filesystem-based storage engine to one that shoves session data into the browser cookie. So if you're persisting large-ish objects across requests in the session, this will fail. Sadly, basic tests may pass, while serious work will break: I found my bulk page transformation
  code to work fine for 20 pages, but break for 180. The solution for this is to add

  config.action_controller.session_store = :p_store

  in your environment.rb file.