**updated to include links to other presentations at end of this post**
Great MSDN article by Michele on the appropriate uses of WCF (focusing on the new features available in .NET 3.5). I just happen to be talking about that same topic today at the MSDN San Diego launch event and have updated my deck to reflect some of the well-written information Michele included.
Bruno's blog - http://www.brunoterkaly.com/
Daniel's blog - http://www.dotnetdoc.com/
Rob's recordings of original launch content (screencasts) - http://www.robbagby.com/robbagby/VS2008Launch/VS2008Demos.htm