Tom.Thomson (9/27/2010)
And transactional replication certainly doesn't create any extra columns by magic (at least in didn't in SQLS 2000), and neither does snapshot replication; merge replication may do it (I've never used it, so never read up on it).
It specifically happens on transactional replication with updateable subscriptions and on merge replication. It is how the system deals with conflicts when two separate sources could in theory get updated at nearly the same time in the same location in the data.