Is there anything about the way you query your data that a traditional serialized object store wouldn't handle? Being that you want it embedded and therefore local, I'd imagine you're talking about relatively small amounts of data and your performance concerns aren't too extreme?
That would be perfect except you need a commercial license if your going to bundle it with a commercial product. Really wish they would just put the pricing on the site.
I'm starting to think you're right. Maybe a traditional serialized object store is the way to go.
Would something like this fit the bill? http://www.db4o.com/s/monodb.aspx