I believe Apple is at a loss too. This problem has been active since Lion was introduced. I've been dealing with it since May 2012. Things did not improve after my iMac was in the Apple Store for 3 days. Their assessment -- problem could not be replicated. Would be a laughing matter if not so frustrating. The whole mess is very Microsoft-like. I won't move to 10.8 until there's some hint of resolution. The whole thing has been a productivity killer. Quite the opposite of what Apple says it's all about.
I have been having this problem with just one of our iMacs in our house. I went through Apple support and navigated through all the twists and turns they suggested to try to get the problem solved. NOTHING WORKED. THEY DON"T KNOW HOW TO FIX THIS PROBLEM. BUT I DO! Unfortunately it involves buying a $30 wireless ethernet adapter (I got an IOGEAR, and I have no connection to their company. Probably any wireless ethernet adapter will work). I turned off the internal airport wireless device and through the network settings in the system preferences connected to my CISCO LYNKSYS ROUTER (which has been bashed left and right in the forums here). THE PROBLEM IS SOLVED!!!!! NO RESTARTING!!! NO DROPPED CONNECTIONS!!!!
So the problem isn't with the router, its with the airport wireless adapter in the iMac. It stinks to have to spend more money after you lay out so much for an apple product, but it sure beats restarting the computer over and over every day.
Hope this helps my friends out there. I can now allow my hair to repopulate my head since I've been pulling it out over this issue for months.
I threw in the towel and ran an ethernet from my iMac to an ethernet connection on my Belkin wireless router.
Result is there are no longer any drops on the iMac and my MacBook Pro, iPhone, and HP Windows laptop are running on my wireless network.
Apple when are you going to be able to address this problem?
Update on my case...
After 2 brand new chrashed iMac 27" on 1 month, Apple gave me a brand new iMac full loaded with all the best components.. NICE
The unofficial explanation from apple was: "You use your iMac to much!" WHAT???
But Apple is right... The i7 models (fat model) simply can't cool the machine on heavy daily tasks!,
and you slowly burn down the components inside..
My symptomes was:
Overheating graphic card
Overheating WiFi receiver
On my last model, the engineers showed me melted components on the motherboard!
My best advice...
Get ridd of your "fat model" iMac i7 and buy the new "slim model", it doesn't even get warm no matter how hard you ride it... FANTASTIC
Good luck to all of you
After a week of trying verious fixes, I realized that the problem with my iMac dropping Wi-Fi arose when a technician from my ISP provider (Rogers) installed a proprietary modem. My iMac and AppleTV started dropping the Wi-Fi, while my iPhone 4 could not connect at all. I have just replaced the proprietary modem with a Cisco one -- and everything is working perfectly. So if you don't have a Cisco modem, get one! There are all kinds of proprietary modems around, and some of them have been tested for Windows, but not for Apple. I hope it helps.
On my MacBook running 10.7.5, the problem seemed to be the TimeMachine drive plugged into the firewire port. That makes NO sense to me, but I can plug it in and pull it out and have no connection and be connected to the house wifi like a switch.
(My computer is old enough that I cannot upgrade to Mavericks.)