P2P is inherently a multi-master system. If you update the same row in multiple peers at the same time you will get an update conflict.

SQL 2008 R2 allows automatic update conflict resolution, by saying the server with the lowest name in the collation sequence wins. You can also get automatic logging of the data that has been lost, so you can decide what to do about it.

We are in the final stages of going live with a P2P environment running within AWS. For us the main benefit of P2P is fast and relatively simple failover.

We have decided to route all our updates to a single node, so that we never get update conflicts. For us this is easy, as all updates are done from our web applications and all web applications use a common connection string to identify the server that hosts the updates. We use a DNS vanity name to identify our 'master write server', so if we have to move updates to another node then all we have to change is the IP address referenced by the vanity name.