The Rails team at XING developed the alter_table Rails plugin to extend ActiveRecord migrations with MySQL’s native ability to run multiple alterations on a table in a single ALTER TABLE statement.
The developers at XING just launched a tiny Rails plugin to replace the Rails default way of using a div to highlight input fields with errors by just using a css class: http://github.com/xing/classy_field_errors. A related blog post explains the problem and solution in more detail.