As for incompatible schemas, we're not aiming to build one big ontology for the world, but we are aiming to facilitate a large number of datasets that are useful by themselves. We're working towards being able to link various Silk sites to each other and will try to find ways to make as many as schemas fit into each other.
As for manual metadata, see: http://news.ycombinator.com/item?id=3953644
As for incompatible schemas, we're not aiming to build one big ontology for the world, but we are aiming to facilitate a large number of datasets that are useful by themselves. We're working towards being able to link various Silk sites to each other and will try to find ways to make as many as schemas fit into each other.