As many have said on this thread, you shouldn't need to marinate a steak unless it's a bad cut of meat. That doesn't mean you shouldn't create your own sauce - in fact I'd encourage it if you don't like the standard bbq sauce and steak spice. So depending upon what type of meat you're serving should determine whether or not you want the meat to marinate over night. A marinate should have something acidic in it to break down the proteins in the meat. This is what make a bad cut of meat more tender.
For a simplified breakdown of meats check out this simple site:
http://johndlee.hubpages.com/hub/Cut..._steak_is_best