Christian Weyer has an article on MSDN Mag together with Steve Maine and Dominick Baier about using Windows Process Activation Service (WAS) for non http protocols. Actually it's about much more than that, but that is what I found interesting. Hosting WCF services in WAS gives you the possibility to use NetTcp, Named Pipes and MSMQ protocols. For more info about WAS you should read the article. Anyway, using WAS as a host for WCF services sounds like a good idea. You don't have to create and maintain your own NT Service and you get stuff like "on-demand activation, process health monitoring, enterprise-class manageability and rapid failure protection" for free. But then you also get some lifetime management "features":

"...WAS does demand activation (as you know, the "A" in "WAS" stands for activation). This means that the application domain hosting a service only gets created when a request message comes in. Application domains shut down again after a configurable idle period. There are also several reasons why WAS or the ASP.NET runtime may decide to recycle the application domain or even the whole worker process."

So I suspect there would be some overhead of creating and shutting down the app domain, unless you can set the idle period to infinite of course. And then you have the recycle bit... Hmmm.... Do I want that?

If I were asked: "WAS or NT Service?", I think I'll go for the NT Service, unless there's something I totally missed out on here... which definitely could be the case <smile>.

If you want to try this out you might find these code samples interesting in addition to the article mentioned.