I am quite interested in Reactive Extensions but I cannot find an up to date tutorial. I started with Curing the asynchronous blues with the Reactive Extensions for .NET but it
When learning Rx the first thing is to understand the philosophy behind IObservable and how it's push based nature compares with IEnumerable. I suggest the following one for a good explanation: A[nother] Simpler Tutorial for Reactive Extensions
Lee Campbell has nice series explaining the api and when to use them. He also tries to keep it up to date with latest releases: Reactive Extensions for .NET an Introduction
The series is now available as a book at Introduction to Rx
By the way, I have also written a blog post about solving real life problem with rx: Using Reactive Extensions for Streaming Data from Database
Hope this helps.