Tests: 2 x MacBook Pro on SnowLep WiFi to Airport Extreme run speed 300Mbit/s - upgrade to Lion then they run at 144Mbit/s. 2008 iMac (not AirDrop capable WiFi card) using Lion runs at 300Mbit/s to same Airport Extreme until MacBook Pros start using same Wifi and then iMac drops to 130Mbit/s. Using Airport Extreme "guest network" feature to swap the iMac to separate WiFI network speed returns to 300Mbit/s. Conclusion: Airdrop on the MacBook Pros sets up its own WiFi network using half the card's resources and drops the main WiFi link speed in half. Do not understand why iMac speed on same WiFi network drop to half when MacBooks with Airdrop are used.