the transporter..of course, the first version I remember was 'the Fly'..the first transporter malfunction..;)
The real reason Roddenberry came up with the transporter was to speed up the action (no long shots of spaceships landing, or shuttles..how far we've come..;)
On the shows, I think the operative word for the scientific displays was 'technobabble'..;)
As for flying cars, think about it..do you want the idiots in front of you on the freeway flying over your house?..;) Mainly keeping something in the air takes too much energy to be practical..at least as far as hoverin'..;)

I wish I'd said that.. The Staircase Wit

anahl nathrak uth vas betude doth yel dyenvey..;)