title: Magento hardcodes VARCHAR attributes to 255 length, any reason to not change this?
body: <p>I have a requirement to save an Order Item attribute as a string up to 400 char. While it could be implemented using a text attribute, I would rather use a varchar(400). However, the <code>_addFlatAttribute()</code> method in <code>Mage_Sales_Model_Resource_Setup</code> hardcodes the length of varchar to 255. It could be changed after the fact by a setup script with DDL, but I'm wondering if there are likely to be downstream dependencies on VARCHAR being 255 char. </p>
  
  <p>Any thoughts?</p>