I was checking the Joomla! 3.0.0_Alpha1 version and got an error after installing one of extension that shows Directory separator constant DS error. So if you get such error for any of your extension try this code
if(!defined('DS')){ define('DS',DIRECTORY_SEPARATOR); }
May be making a system plugin can solve this problem. I developed one đ
Fix DS error in joomla 3.0 (1.3 KiB, 1,747 hits)
BTW, we develop custom joomla extension at codeboxr.com