Well.. Winforms does not have a "dispatcher" scheduler. Instead there is a `ControlScheduler` which should be used to schedule operations on the UI thread. A `ControlScheduler` makes use of the `IsInvokeRequired` method.

Since ReactiveUI should work "out-of-the-box" I've defaulted to use the `WinformsSynchonizationContext`.
The `WinformsSynchonizationContext` can also be used to schedule operations on the UI thread. I've used a `SynchronizationContextScheduler` as "default" MainThreadThreadScheduler because at Registration Time I can not create a `ControlScheduler`.