For What it is Worth
I had experienced wifi drop problems after updating to 10.7.2, late last year. It was really frustrating few weeks, which lead to a frantic search for solutions.
I had found an answer in the following link, which I had used. It was successfull, and I never faced wifi drop problem again.
Two weeks back, my imac auto updated to 10.7.3, and wifi drop problems resurfaced again. Initially I didn't realize it was related to the update. However, once I thought it could be, I searched and found that the wifi drop problem is again happening with 10.7.3
Luckily, I had bookmarked the link, and had the local copy of the details of the earlier fix.
I tried the same with 10.7.3, and to my great relief it works.
No wifi drop after this fix applied on top of 10.7.3
My system is 27 inch imac, late 2009 model.
I credit all the thanks to the original contributor of the fix in the link.
As I have seen so many frustrated users venting their ire with respect to this problem in this forum, I want to share my experience and a possible solution/workaround.
Please try and share your experience with this approach.
http://rys.pixeltards.com/2011/09/04/osx-lion-wifi.html