Just for information of the thread, I have a new mid-2011 MBAir (4.2) with Lion which also experienced this problem straight out of the box. As described here, I have the same symptoms of appearing to be connectedd but not being able to send/receive. The only way I can resolve this is to disconnect and reconnect to the access point. Sometimes (like now) that will be ok for 30 minutes or more. Other times, it will drop out straight away again.
As I've posted in one of the other threads, the thing that annoys me about this is that there are so many forum threads dedicated to this all over the internet (for many years), but there appears no action from Apple on it - preferring to ignore it's customers problems. While I've been a Apple user for a few years, this is my first Mac purchase and it has left a bitter taste in my mouth to say the least. I've been using a MBPro for a couple of years and never had any such problem (in the same network).
Also for information of some of the other posters - I experience this on a 'G' access point, so the issue is not isolated to N/G switching. Additionally, 'N' WiFi in itself does not necessarily have shorter range through walls - 'N' operates on two frequency bands: 2.4Ghz and 5Ghz, while 'G' operates on the 2.4Ghz only. While certainly the 5Ghz band should get poorer penetration through walls and other obstacles, the advanced technology used in 'N' WiFi should more than be able to make up for that - it uses very sophisticated muti-path signal recombining and other tricks which should make it effectively more sensitive and able to sustain much higher data rates despite significant signal attenuation. Depending on the particular obstacles and range you're talking about though, each case can be different.
I've done some network captures on my problematic MBAir, and at other points in my network to see if I can identify the problem. Once I get the phantom dropout happening I notice that my Air's WiFi can still receive network traffic normally, as it sees all transmissions from other network devices around it. Also, it thinks it is still connected to the network (as it should - the network manager shows an active connection) and it tries to send packets onto the network when you make particular requests. It appears to me that these packets never actually make it out into the network, and it just keeps re-trying until it eventually times-out.
While I accept other causes are possible, this leads me to believe that the problem is with the Broadcom wireless driver. As for how the same problem can be faced by many different generations of Mac - I would hazard a guess that it is likely that, always having used Broadcom WiFi chips, that there are large parts of shared code between the driver for various models, allowing for problems to be inherited down generations. Identifying the specific issue in the driver leaves many and complex possibilites, so I won't speculate further here, but it seems like a good place to start.
Apple? Where are you on this?
