On the actual GMAT are there any repeat questions from the review books or are all the questions new in the sense that they were never seen?
No, the OG books contain only retired questions. But if you see any source that claims to contain real, un-retired problems, then avoid them like the plague. There was a huge scandal about this not too long ago.
If the questions are all new do they all follow the format of the GMAT review?
The format and presentation are similar. But don't worry about that right now. The most important thing is to fully understand the concepts and practice with the OG.
Should I expect my score to go up by 10% or drop by 10%? Do people who take the exam see an average of an increase in their scores over test practice or a decrease?
The general consensus is that GMATPrep accurately predicts your actual performance within a 30 point range (both above and below). After the second practice test, though, the score may overestimate your performance.
I always assumed that my real score would drop. That way, I would study as much as possible to do well on the practice tests and stay mentally alert for the real test.
Along with YourDreamTheater's suggested link, check this one out as well for general reference:gmat-scores-guide-to-gmat-scores-score-reports-83890.html