I follow Zend Framework (PEAR) class naming conventions, and my user table class should be named User_Table instead of UserTable and be placed in User/Table.php instead of UserTable.php. Since Table suffix is hardcoded, it's not possible to do that.
I added ATTR_TABLE_CLASS_SUFFIX attribute and set it to Table by default, so that existing code is not affected. Now, if I want, I can change that prefix to _Table and be happy. The patch is attached.