Apple Lion OS X 10.7.3 Update Wifi

Solution 1:

Many times the Combo Update will resolve problems. Download that update (on another system if you have to) and install it, then restart. I have not seen generalized WiFi issues after the 10.7.3 update, so it is very likely the combo update will help.

Solution 2:

I had the same problem even with the combo update. I was able to find a thread on Apple's support forums that described the solution as turning off and on the OS X firewall, however, after booting from Windows (Boot Camp) back into OS X, I found that the issue had resolved itself without further intervention.