I guess as a caveat, you may be given work that seems like it's out of your depth, or you have no idea where to start. People will gladly help you, but at the same time, there is only a bit of direction. Most of the "important" (I say that loosely) is done by the more experienced members, so try to learn from them because when they leave, you will be there to fill their shoes.
The other thing is that they usually meet up on saturdays (elec) and sundays (mech) to do work. Prior to the race last year, we also had some meetings during the week.
It was definitely good experience though.