Well, I hate to be a pain in the bu@@, however I have had the same issue as many folks with the wifi disconnecting when the IMac wakes up. All this happened after my upgrade to Lion. The internet is full of fixes, including going into files and deleting reinstalling the os, etc. My router is current technology and is functioning perfectly.
The whole reason I purchased Mac products was to get away from techinical issues, conflicts and config problems which are common in Windows PC's. I just want the thing to work without having to perform risky file system tasks.
With so many folks having similar problems,what is wrong with Apple --that they can't develop a simple patch to fix the problem of the wifi disconnecting on its own.
I wish there was an easy way to reverse the Lion upgrade (just like your can uninstall a Windows upgrade).
I also own a Macbook Air with Snow Leopard, a Windows based PC, Ipad, and I phone-- and not one of them has this problem with connectivity to my router.
Come on Apple---you have the cash on hand and the resources to fix this problem. As a leader in this field, you should be embarrased by all the chatter relating to this issue.