It's hard to say whether the real tests were easier or harder than the practice tests... Afterall, the practice tests were given as real tests at some time I think and had very different difficulties. One factor may be that after 400 questions of preparation, the questions just look easier to us. For instance, when I first looked at the practice tests I had no experience with logarithmic paper. But after realizing it's important, I learned it and answered the one related question on my October test in 10 seconds. If I hadn't reviewed that topic, I would've looked at the question on the real test and shouted, "There's a misprint on this booklet, the gridlines in this graph are uneven!"
Regardless of the difficulty, ETS supposedly has statistical methods to assure the scoring scales are fair... I looked a little bit into this because I thought that the students taking the October test would be on average stronger/more prepared and was worried my score wouldn't be as high than if I took the November one.
It may seem impossible (it did to me) to make an objective scale based on how difficult they 'think' the questions are and how smart they 'think' the students are... but it might work somewhat like this (I could be completely wrong but I hope at least to make it plausible to other test takers that fair scaling is possible.)
The test has 100 questions. Suppose 25 are questions recycled (either verbatim or very similar) from earlier tests (much earlier, and these would of course be questions not released in the practice tests). ETS could then compare how the 11/3/07 students scored on those questions and then make an objective measure of the abilities of this new population compared to the old one. Then, knowing the student's abilities, ETS could analyze how they performed on the other 75 questions and come up with an objective measure of the difficulty of those questions, and thus the whole test. Combining this data, they could set the raw score vs. scaled score levels in an objective way that does not change over the years. That's why they say an 820 today is equivalent to an 820 earned in 1991.
The precise way they do this (called equating) was rather vague on wikipedia and ETS's websites so I made some guesses but if what I said makes sense then I'm sure they have even better ways of doing it. But overall, nobody should be concerned about their test being too hard or easy.
--- yeah the scores are read by a robot. But don't fret over that, I guarantee you that robot was much more competent than any ETS operator I've ever spoken with, haha! The $12 is indeed just another ETS extortion.