Apple has released firmware updates that might improve WiFi/AirPort-stability on your 2011 Mac after the OSX 10.7.3 update :
Mac mini (Mid 2011) EFI firmware update 1.6
http://support.apple.com/kb/DL1500
MacBook Pro (Early 2011) EFI firmware update 2.7
http://support.apple.com/kb/DL1499
iMac (Mid 2011) EFI firmware update 1.9
http://support.apple.com/kb/DL1498
MacBook Air (Mid 2011) EFI firmware update 2.4
http://support.apple.com/kb/DL1497
MacManus.nl 