I purchased my first mountain bike in 1992 and worked in varies levels in the biking industry from 1995-2004. Here are some trends, changes, and parts that I simply do not care for (either as a rider, mechanic, or enthusiast).
-Alloy Freehub Bodies...DUMB...save 80 grams but you have to run expensive cassettes (a high wear item) on them. For some reason if you buy nice hubs, you get stuck with these (Chris King actually offers a Stainless Steel FH Body). They're just a bad idea unless your a uber weight weenie. It'd be nice if more high end hubs came with a Steel or Ti option.
-9 speed...yes, like most I use it. And it has gotten pretty reliable BUT...it was a solution for a problem that never existed. We should have stayed at 8 speeds, at least my chains would last longer! EDIT: 2011 will bring 10 speed drivetrains to the masses from both Shimano and SRAM...when will the insanity end!!!!
->$600 suspension forks...really, have they improved our riding experience that much? I still have as much fun on my $300 fork as I had on a $600 fork I owned in the past (and work on it less). Some things just don't need to get this complex
-Downfall of affordable Steel...OK, its making a bit of a comeback in the 29er and SS market. But it never should have gone away. Simply put, steel is durable, comfortable, and affordable. It also isn't that heavy, lets face it...most of us should be more concerned about how much WE weigh than our bikes. I'm hoping to be back on steel for my 29er soon and I refuse to ride anything else on the road.
-Prefabricated Wheels...Most use proprietary parts that are difficult to find and very expensive. You can get a hand built wheelset using better hubs, standard spokes, and standard rims for the same price that will be just as durable, just as light, and way easier to service.