British Airways recently operated one of its 747-400s (G-BNLR) for about a week without the winglet on its port wingtip. The winglet had been removed having suffered minor damage on the ground and has been replaced.
BA says it is "perfectly acceptable according to the Boeing dispatch deviation manual" to operate without one or both winglets, which are mainly induction drag reducing devices. BA says handling is virtually unaffected, but the aircraft suffers a 2.5% fuel penalty and 9.5t maximum take-off weight penalty.
Source: Flight International