This weekend I played around with this, and created a couple of POCs to get a feel. And I'm loving everything. Reactive extensions (Rx) is really cool, as it introduces lot of new possibilities.
Here is the essence and summary.
.NET Rx team (this is not an official name) found that any push sequence (events, callbacks) can be viewed as a pull sequence (as we normally do while accessing enumerables) as well ? or they are Dual in nature. In short observer/observable pattern is the dual of enumeration pattern.
So what is cool about about this duality? Anything you do with Pull sequences (read declarative style coding) is applicable to push sequences as well. Here are few aspects.
You can create Observables from existing events and then use them as first class citizens in .NET ? i.e, you may create an observable from an event, and expose the same as a property.
As IObservable is the mathematical dual of IEnumerable, .NET Rx facilitates LINQ over push sequences like Events, much like LINQ over IEnumerables
It gives greater freedom to compose new events ? you can create specific events out of general events.
.NET Rx introduces two interfaces, IObservable and IObserver that "provides an alternative to using input and output adapters as the producer and consumer of event sources and sinks" and this will soon become the de-facto for writing asynchronous code in a declarative manner.
The source code as part of the second article contains a drawing application in WFP, with a version of System.Reactive.dll that I rebased to target .NET Framework 3.5 using Reflexil - You should be able to open the same in VS 2008 to play with Winfors or WPF
Check out this set of articles where I've posted my thoughts