Adding unnecessary verbs to the standard does create problems, but having a few standard verbs and controlled customization is fantastic. The trouble with custom verbs, like you touched on, is the inability to advertise their contract. I would argue that the OPTIONS verb does not give back enough information to make it useful. Either the OPTIONS verb needs to return more information, or an additional verb should be standardized to allow for discovery and use. The level of specification is a good debate to have, because WS-* was to much specification and REST is almost too little.