The reason `error_messages_for` was pulled from Rails 3 is a new guideline that says that nothing in Rails Core should dictate the look and feel of an app.
Okay, that's all well and good. How do you fix this problem? There are two ways. The first is to implement your own error handling. A HAML snippet:
This is by far the best way to go about it. However, if you have a current Rails 2 app you're upgrading, writing your own error handling may be rather difficult or time consuming. In that case you can install a plugin that restores the original functionality of `error_messages_for`.