Does this mean everyone holds a copy of the data? Would this not become very client heavy?
No, the content data itself is distributed across the File Transfer networks (i.e. BitTorrent, MaidSafe, Storj, etc) independently of Bit451. The Bit451 Database metadata (i.e. the core of Bit451) has a replication method modeled on the concept of communities and community-based trust, meaning that you only replicate records from the accounts in your community. Thus the total [meta]data stored per node should be very light. Does this answer your question?