My friend Kirk has a very interesting post that uses LINQ to turn an XML RSS feed into a JSON service using WCF. (Wow, this is acronym heaven!)
The piece has good information about techniques using .NET 3.5 including LINQ to XML (including XDocument) and something in System.ServiceModel.Syndication called WebGet.
I'm still trying to get my head around using LINQ in (Web) services, so this is great.