Uno wouldn't be obsolete, I read a paragraph somewhere saying the UNO was released to coincide with Arduio 1.0,
the revisions are hardware only i'm pretty sure.
MEGA was revised to add some more pins ( not general IO pins ) in the corner, and maybe some other stuff.
Uno was revised due to the reset problems associated with upload, and maybe some other stuff too.
MEGA is no faster, infact it is slower.
ATMega2560 uses an extra cycle with conditional statements, and UNO does something else faster too. ( due to the memory address lengths )
So code on a UNO will be smaller and faster,
the uno revisions are the same physical pinout.
I think the MEGA moved a pin header to match UNO's board layout,but pins are the same.
This shield has the 1.0 standard pinout that consist in
That is an unfinished sentence. and no, I'm pretty sure all UNO shields will be fine on MEGA.
By taking a look at the photo of the motor shield (http://arduino.cc/en/Main/ArduinoMotorShieldR3
) I see that there're two input plugs in there (white color) named 'In 2" and "In 3". In the schematics these point to "A2" and "A3". I assume these are A2 and A3 of the underlying Arduino board, right? So I can use these for my own purposes (not related to the motor shield per se).
Yes the shield is simply bringing the pins up for you to use, look in its instructions, some sheilds may share pins.