WCF - Absolutely Amazing
One of my biggest passions in the development world has always been networked programs. For the longest time I've had bitter sweet feelings about Remoting in .NET. Basically, remoting is one of the most beautiful and powerful architectures that .NET has pioneered. The one issue that I've had has been that Remoting in .NET was limited to a "one-way" architecture.
I can't even explain how excited I was when I learned about WCF (released in .NET 3.0 about a year ago) and the "duplex" capabilities thereof... take five minutes, read this article: http://www.codeproject.com/WCF/WCF_Duplex_UI_Threads.asp