Relatively new to patterns, let me straight away show an example in the context of WinForms.
I have a basic MVP Passive View structure, which one should I go ahead with:
The Presenter should know about the Model, the View should not. A presententation layer is a good idea in many user interface applications. A presentation layer is simply an adapter. It presents an interface that's easy for a user interface layer to use (i.e., it presents lots of events, bindable properties, and so on) while obscuring the underlying data layer. This makes the data layer easier to re-use.
EDIT
So why can't the view just talk to the model directly? It certainly can. The problem is that there is usually an impedence mismatch between the model and the view. In other words, the programming interface that's natural for the view to use does not match the interface that's natural for the model to expose. If you adapt the model to suit the view's needs, then you end up creating a strong coupling between the model and the particular type of interface you're using.
For example, your app might be a GUI app today, but what if tomorrow you're asked to produce a version for the cloud? The events and bindable properties that are helpful for Winforms will just get in the way when you try to switch to WCF Rest. If you use a presentation layer, then adapting your code to the new environment will be much easier.