I am currently working through the source code to add phpdoc documentation to ease development. You can access this documentation through the wiki (http://doc.silverstripe.com/doku.php?id=all-classes). I am starting with the core classes such as DataObject and ViewableData, but if there are any classes you would find particularly helpful to be documented, please add them to the documentation requests page (http://doc.silverstripe.com/doku.php?id=documentation-requests).

Thanks!