Having used OpenAccess on several projects, I must say that it meets all the above criteria.
One system I worked on was based on WCF services talking to several client types (smart, web, other WCF services, etc.) Through a layered architecture the WCF services used OpenAccess as persistence mechanism.
I am especially fond of the scaling that OpenAccess performs.. The intelligent Level 2 cache (L2 cache) does a perfect job there and it is of cause distributable.
Actually I wouldn't call OA heavy weight... You don't even inherit from a base class. Also it is a big plus that there are tools to perform the day-to-day developer tasks (create a new DB schema, merge schemas and so on) integrated into visual studio.
