Winglets..are they usefull?

[TruBlu351]

A 777 had decades more technology in its modern wing that the 747. They are quite different wings aerodynamically.

Look at the new Boeing 747-8 and 787 wing design. No giant winglets, but their design is much more efficient. More of a slender raked design at the tips.

http://www.boeing.com/commercial/747family/index.html