.NET remoting will continue to exist in Longhorn and beyond, since backwards compatibility is always a key requirement for our operating systems.
The thing is the product group that owns the Remoting, WebService, and COM+ technologies has made the decision to invest all future enhancement efforts on the WebServices technology. The reason is because of the existence of the broad industry adoption of the standards, we're able to make WebService technology better in ways that is logistically impossible with the other ones, but there aren't reasons why the WebService technology can't be made every bit as good as Remoting and DCOM.
So basically Microsoft is encouraging customers to transition to using WebService technology because it's the technology that will continue to improve.
Today, there really isn't much in terms of features in Remoting that you can't get with using either WebServices or COM+. Maybe over Webservices, but not really over COM+. However, there are still some distinct features that COM+ has over WebServices. So that's why they say COM+ is fine if you need some of those extra features not yet available with WebServices.
Because COM+ is still very widely used, they plan to try and offer really good code migration strategies from COM+ to WebServices, but they're not planning on creating as good of code migration strategies from Remoting to WebServices. So that's another reason why if you need more features then WebServices can offer they are encouraging using COM+ (versus Remoting).
They expect the gap between the features offered by WebServices and by COM+ or Remoting will be closed when Indigo ships. So at that point you'll likely want to switch to WebServices because they expect it will have all the features that COM+ and Remoting have to offer and more.