Paul Fallon posts some good news (and excellent description) about Enterprise Services in .NET 2.0. Systems.Transactions already features Transaction promotion and delegation using the concept of PSPE (Promotable Single Phase Enlistment), in particular with SQL Server 2005 which is the only current database RM (resource manager) that supports this. The good news is that Enterprise Services will also have this feature. That's great, especially if you already have existing ES code you want to recompile and move forward. Go read Paul's post for more information.
On a slightly related note, I noticed recently through Reflector that Systems.Transactions references System.EnterpriseServices in its assembly (Systems.Transactions.dll). I know that S.T uses managed calls to MSDTC when a transaction has been promoted to a full distributed transaction, but I wonder if ES is still in the mix somehow as a ServicedComponent wrapper?