I would say that in general, cheap crap has fallen off a cliff. Why? Maybe the economy, but more likely due to the HUGE amount of items being offered at no reserve on a weekly basis (eMoviePoster, MPB, and others). With so much decent quality material available at reasonable prices, why "waste" your money on marginal stuff? Also, I used to sell tons of cheap stuff to people who re-sold it at fixed price on eBay. One by one all those people are closing down due to the eBay implosion.
Medium range items are somewhat spotty. Condition is important, and there are changing tastes, especially for lesser titles of major stars, or items with uninteresting images.
But truly good items are doing fine, UNLESS they are the kind that are offered over and over and over, or if the seller wants the highest price it ever sold for. Also, collectors are getting more and more wary of restoration and fuzzy images and fuzzier condition descriptions, so most of the best prices are reserved for truly rare desirable items in really nice condition, the same as it ever was (the same as it ever was).
I stand by my position that the last time it was as good a buying opportunity in posters was in the mid-1980s, thanks to a huge supply and many (but of course not all) motivated sellers. The trick is to find the good buys, but if you do, I think you will look back in amazement in five years at many of the great deals that were available.
Bruce