You know, I was trying to think before of a sport where there were more 'debatable' decisions handed down.... but I couldn't really think of any. Most codes of football (I'm talking league, rugby, AFL etc) have some line-ball decisions, but comparitively few to cricket. Soccer's normally pretty clear (apart from off-side decisions). The only possible exception is tennis with line calls (but it's normally the players who try and 'create' a debateable decision, anyway). I'm not exactly sure what point I'm trying to make here, but I think that cricket is probably the most difficult sport in the world to adjudicate. From no-balls (both front-foot and height wise), to lbws (about 10 different factors), to hearing the snicks, to adjudicating on catches, to keeping the score... I'd challenge anyone who said that cricket umpiring was an easy job.
I think that if the third umpire can prove that the batsman was 'not out' when given 'out' within the allocated 2 minutes (I think - someone correct me) before the next batsman is due on the ground - then he should be called back. Alternately, if he was 'out', and wasn't given, then the third umpire has until the end of the over to give him out (would be an interesting situation if you're the batsman and nicked the third ball of the over to the keeper and was given 'not out' - because you know at the end of the over the third umpire will probably give you out... you'd just the smashing the crap out of it!).
I know this probably wouldn't work, but it's something to think about.
However, I do think that there should be some system of calling the front-foot no balls - surely some technology can be used for this to free the umpire up a bit????