Here's what I think:
> 5yrs ago vs Now: Quant has gotten considerably more challenging, Verbal is about the same, albeit with a slightly different focus - much of the difference is related to how global the test has become (e.g. less idioms in verbal, making for a more level playing field)
<5yrs ago vs Now: Difficulty has not changed materially; however, the scoring algorithm has been re-calibrated, IMHO penalizing more for each wrong answer, and requiring progressively higher accuracy rates to hit the same scores
Creative Speculation: The new policy allowing users to see their score before they submit it can potentially drive up the average score and thus continue to ratchet down the scoring curve until a point where the GMAC will need to revamp the test with even harder questions :0
Of course if they include cancelled scores in the avg, than this is much less likely