wing length and winglets

[benters]

I guess a certain amount of wing length is determined by the weight the aircraft is going to be fully laden, but how much over size is needed ? also if the winglets are a good thing then how come they don't feature on the tail section ?
the other half and I were looking at the A380 in front of us at Heathrow and its a mighty thing, but it looks out of proportion which lead me to seek out answers from the wise folk on here. . .

[benters]

Thanks for the info guys. . . .
G-PEEK is an interesting looking bird