Taking notes on slides on a smartphone

I was browsing some simple apps that could help students in class,
when I came up with the following idea.

Suppose the teacher is using slides (e.g. PowerPoint) in his lecture.
These slides are mostly availabl on the teacher's homepage, blackboard or somewhere on the net.
Now as a student you feel these slides are not 'complete', maybe because there is not enough information on them, or the teacher is adding some extra info to his lecture, that is nor on the slide nor in the course book.
So you want to take some extra notes on one or more slides.

I have found some note taking apps (Notes is standard on iPhone, Simplenote, Evernote, WriteRoom, etc...)
Which one of  these is the best note taking apps I cannot conclude, since I am not able to test them.
But I think it depends on your personal preferences and needs anyway.
However, none of these implement a feature where you can stick notes to some or more slides.
(I read something about sticking a note to some image, but I feel it's not the same, since it's just a single image, probably not containing any text)

So I searched for an app that presents slides in a manner that is suited for smartphones.
Keynote (+ Keynote Remote) is a good app for iPhone for creating and giving presentations:
http://www.apple.com/iwork/keynote/#flexible
This app is intended for the presenter, however, the creator of the presentation. Not the ones following the presentation.
The app allows the creator to add notes for himself to the slides, and it has lots of other features.
With some simple adjustments I believe that this app could be used by students as well to take notes related to one or more slides of the presentation.

Example of a slide with extra notes

Here is a short video that presents just the features needed for the above idea:
http://www.youtube.com/watch?v=nBzXUWgl9T0