first thanks for the detailed feedback.
1) Controls.
Really: we ship with default controls up/down arrow for acc/brake and mouse
to steer??!
Did someone try to use it like that? I've almost tied my arms trying to
race with this configuration (really unconfortable).
I suggest to use up/donw arrow for acc/brake and left/right arrow to steer.
I know keyboard for a sim is not the best input hardware but I don't think
our current configuration is any better and for sure not common on other
sims as default.

I actually use mouse steering for testing, and for it to work well mouse acceleration should be set low in the OS, which probably is not when one first tries SD. And I use A/Z for accel/brake (since Grand Prix 1), which is more comfortable. But I agree that the 4 arrows are a better and more expected combination first.
1.2) key definition screen (the one that appear when you press f1 in race)
First how do one know it is under the f1 key? I expect something like this
to apper as a voice in the "esc" menu near the adjust controls option as
"Other controls" or something like that-
Zoom options are put everywhere some seems also to be double
And what the hell do the "SPACE: skip prestart" one I have no Idea
see http://i.imgur.com/d2js57j.jpg

Right, it should appear as 'Help' or something similar in the menu. But after the release.
2) SD by default start in windowed mode and in a low resolution. I was
expecting a full screen bigger resolution. (there is probably a tecnical
reason for this I suppose)

If I remember well, the reason is that screen size detection does not work well on some systems. And I actually prefer it this way.
3) The mouse cursor is always visible on race. And on race start it is in
the middle of the screen: very annoyng (I know you can hide it with "O" but
i dooubt new user know it).

Here I do not remember whether it is this way on purpose or not. If yes, the reason might be to give a visual clue about the steering wheel, as not all cars and views have an animated one.
4) Auto gear change and autoreverse are activated by default (OK with
that). But it seems autoreverse doesn not work realibly (BUG?, dd someone
else experienced this?)

I will have a look.
5) Forza as default quick race track is a framekiller. I know Forza is a
really nice track but it really kill performance, even on my GTX770 with
max settings I get around 40 fps with some noticeable drops. Not sure if it
is the best choice, it can give a user a bad idea of the performance of all
Speed Dreams

Good point, I suggest Espie, especially that it is the default track.

From a release point of view, I think only points 1. (Controls) and 5. might be small enough changes to do in an RC, only if a rebuild is necessary.