Erik Meijer: Rx in 15 Minutes - Rx is Here!!!!!

As Rx is a library to orchestrate, not perform asynchronous operations, you would use the Async IO features from .NET and use Rx to react to the completion of the IO:

standard async IO:

var fs = new FileStream(@"d:\temp\test.txt", FileMode.Open, 
  FileAccess.Read, FileShare.Read, 1, true); 
var data = new byte[fs.Length]; 
fs.BeginRead(data, 0, data.Length, (result) => 
{ 
  var bytesRead = fs.EndRead(result);
  Console.WriteLine("{0} bytes read.", bytesRead); 
}, null); 

with Rx:

 
var fs = new FileStream(@"d:\temp\test.txt", FileMode.Open, FileAccess.Read, 
  FileShare.Read, 1, true); 
var data = new byte[fs.Length];
var asyncRead = Observable.FromAsyncPattern<byte[], int, int, int>(
  fs.BeginRead, iasyncResult => fs.EndRead(iasyncResult)); 
var result = asyncRead(data, 0, data.Length); 
result.Subscribe(bytesRead => Console.WriteLine("{0} bytes read.", bytesRead)); 

Now this is a small  sample, but the main difference is that in the latter, the result of the async operation is a first-class value. This means that you can pass the event stream around, do various operations on it (such as select, merge, selectmany, zip etc...), post the result to the UI thread, etc...

http://msdn.microsoft.com/en-us/devlabs/ee794896.aspx