I wrote a blog a while ago that Commerce Server SP1 with SQL 2005 SP2 supported replication with Profiles and transaction database. Now I can confirm that this is a supported scenario here is the KB Article. I am disappointed that the KB article does not walk the user step by step and setting up your profiles and transactions database but at least you know it's supported scenario.
What about replication of other Databases?
Marketing, Product Catalog, Transaction Config and Inventory is supported by use of Import\export APIs and\or using Commerce Server Staging.
Why Use replication?
Multiple data centers for backup and redundancy.