This only applies to the 2011 interface, the CRM 2013 interface is COMPLETELY different.
I am new to customising CRM online and have come to it since the December 2012 Service Update that included the ‘Updated Forms’. The interface that the ‘Updated Forms’ provide is much more in keeping with the 2013 generation of SharePoint and Office 365 products and would therefore be my first choice for a general CRM UI style.
As it turns out the ‘Updated Forms’ are in fact classified as ‘Read-Only’ forms with controls on the page to allow the in-place editing of specific data. This type of form is not the same as an ‘Editing’ form which is what the ‘Classic Forms’ are. There are significant restrictions imposed on the ‘Read-Only’ forms because of the use of the in-place controls for editing:
This adds to the confusion in the interface and in addition prevents the usage of one of the key features that the ‘Updated Forms’ enable, namely the ‘Sales Process’.