Last fall I started having problems with wifi on my 24 inch iMac. For no apparent reason I would find that I could not gain access to the Internet. At first I thought it was the DSL provider and/or router. But no. That wasn't the case because I could access the internet from other devices.
Turning to Google I find there are several Apple forum threads on the topic going back to 2006. Lately, the topic has moved on to include the 27 inch iMac running Lion. It's something I've been tracking for a while in the hope that a fix would turn up from Apple but so far nothing has worked with any degree of certainty. It doesn't seem to matter whether you're running Snow Leopard or Lion, the same or similar symptoms can be replicated across different iMacs.
Looking at the lastest thread I see it has been viewed more than 77,600 times with 180 replies. I take that to mean an awful lot of people are either having the same issue or are at least interested in the topic.
Most people believe the problem is software related rather than a hardware fault. One of the more common suggested solutions is to downgrade the wifi. Another suggestion is an SMC reset. Other suggested solutions are more convoluted requiring the user to alter network settings. Yet other solutions suggest using an AirPort Extreme. Then there is the 'don't use wireless, use ethernet' suggestion. All represent valiant efforts to solve this long standing problem yet none seems guaranteed to work for more than a short while.
One of the difficulties is that the issue appears to be intermittent. Access will be fine for a period and then inexplicably fail. That happened to me this week over several days. It is frustrating when it happens.
Apple has made various statements to those willing to go through the grind of calling technical support and running the gamut of official solutions. One suggestion Another was that it is Lion specific and would be fixed in a patch release 10.7.3. If a fix was included then it doesn't seem to have had the desired effect. Some users have ended up returning their machines for refund. It is that bad.
Apple gets plenty of kudos for its inventiveness across a number of dimensions but this is one problem Apple doesn't seem able to resolve. Pixtonr puts it succinctly:
the update has made my Wifi connection worse.
Now whenever the Mac goes into sleep mode when it wakes i have to manually connect to the Wifi to get it to work.
sort it out Apple.
That kind of says it all.