gt

@dmarsh: good point - compiler could figure out serializable & mbr types

Wonder why the remote queries weren't using the QObservable "provider" where expressions & values were remoted rather than type references...

Yes, you can unsubscribe. You don't need to use another thread, but given the ToObservable() method you do.

public static IObservable<T> ToObservable<T>(this IEnumerable<T> xs) {
 return new Observable<T> () { Enumerable = xs };
}

Here's the internal class needed to handle subscription:

internal sealed class Observable<T> : IObservable<T> {

private readonly UnSubscribe _unsubscribe = new UnSubscribe (); 
public IEnumerable<T> Enumerable { get; set; } 
public IObserver<T> Observer { get; set; } 
public IDisposable Subscribe(IObserver<T> o) { 
Observer = o; 
ThreadPool.QueueUserWorkItem(Worker); 
return _unsubscribe; 
} 
private void Worker (object state) { 
foreach (T item in Enumerable) {
 if (_unsubscribe.Cancel)
 return; 
Observer.OnNext (item); 
}
 Observer.OnCompleted ();
 }
}

And here's the IDisposable internal class that flags when the subscriber is no longer interested:

internal sealed class UnSubscribe : IDisposable {
 public bool Cancel { get; set; }
 public void Dispose() {
 Cancel = true;
 } 
}