1. The Minority Report hologram computer that lets you move things around with your hands -- Seems sort of labor intensive, no? When I'm dicking around on the computer I don't need a workout. Just some mouse clicks and key macros will do just fine for me, thanks.
2. The death ray -- If I'm not to be trusted with a gun, something that gives its unintended victim a chance to live, I really shouldn't be messing with no death rays.
3. The tunic -- They don't have pockets, and although I have no fashion sense it would be sort of depressing to look in my closet and see nothing but metallic tunics. How would I let people know I like the Arizona Cardinals without having to talk to them?
4. The holoband from Caprica -- Mario Kart and Tecmo Bowl are addicting enough. I don't need to be plugging in to a futuristic Second Life that's even more of a time suck.
5. Hovercars -- Every now and then I'll screw up when I'm driving and hop a curb. Translated to air driving, that would mean a 54-car accident that ends in death for all. No thanks.