I've been speaking today in Falkirk (Scotland) and have been asked "what's the difference between Standard and Enterprise editions of DPM?" - the answer lies on the Data Protection Manager 2007 Licensing page which goes into great detail regarding the options for purchasing System Center Data Protection Manager.

In short - the Standard Edition Management License only allows you to back up fileshares, the Enterprise Edition Management License adds integration with SQL Server, Exchange, Sharepoint and Virtual Server. The Enterprise edition also gives you DPM to DPM replication too.