I've posted about this namespace in the past, and its no secret I think this is a great feature in .NET 2.0; one of my concerns though was the behaviour which SQL Server 2000 had with the new stuff. Currently, when you use ADO.NET transactions in 1.x, the transaction is 'local'; so it remains in-process and as such is comparatively fast...if you use SQL Server 2000 with System.Transactions however, the transaction is farmed out the the MSDTC...which actually reduces performance over ADO.NET Transactions. With this in mind, a great example has popped up on Jim Johnsons blog with a 'shim' which aims to overcome this problem...not an 'official' solution...but pretty interesting noentheless!
Should also mention...Jim's blog is just the best resource for any System.Transactions stuff around; the Transactional NTFS bit he posted just looks amazingly cool!