I was just being tongue-in-cheek about the 20 min separation. But as we all know, there have been several fatal accidents involving small planes behind medium aircraft (B727 etc) so they will have to look at the current separation criteria, although the A380 probably generates a similar amount of wake turbulence to the 747:)

All the test conducted with the A380 for the certification and wake vortex limits showed how limited the system of fixed seperation is. Sometimes it works well as the seperation is normally quite large, but sometimes it doesn’t. I don’t know if the ICAO requires seperation for aircraft which are not on the same flight path. Theoretically, with given wind conditions, there alsways exists a “no-go-area” behind an aircraft changing its shape with wind and weight-relation between the aircraft. An 380 could pass behind a B737 with 5m distance, while a CRJ200 may need a 3 minute seperation on a parallel or crossing flight path when an A380 leads.

The A380 produces on average 20% stronger wakes than a B747, although it is about 50% heavier. The B757 is known to have particularly nasty wakes (for its size).