I'm with Applespider on this one. The world travel kit is pricey but the quality of the plugs surpasses any multi-adapter set you can buy at Radio Shack or Sharper Image.
Particularly with those monster UK plugs, exactly as described, but also when using european power strips or sockets where the plug is recessed in a deep well. On more than one occassion, the Apple adapter was the only one I had which would work.
Using universal adapters or the multikits is often functional, but you'll be perpetually dealing with plugs falling out of walls, fitting too loosely, or needing to prop up the power brick against the wall with some weird rube goldberg/tinkertoy construction built from supplies you've scavanged from your hotel room.