Having a similar problem with Airport Extreme -newest version and also Airport block..? the 99$ unit, My MacBook Air newest 13 inch version and my MacBook Pro both get dropped from the wireless. have had no issues for months and months until I upgraded to 10.6.5. My connect will come back eventually but will drop again without warning. It sometimes helps if I turn the wireless off and then back on.
So, I changed my security to WPA2. Works now. No problem. It is a shame that this spec changed wasn't publicised much. It would have saved a lot of people time. Then again, I don't know many people other than myself who run a wireless N network only... Thanks for the info!