I recently got a new iMac (27") and I am having an ongoing problem with wifi connection. It should be noted that other Apple devices -- iPad, iPhone, MacPro laptop, and Apple TV -- do not seem to have any trouble. Nor did my old Mac Pro. But the iMac connection keeps dropping. I have researched this issue in the Apple Support Forum and followed much of the advice, e.g. establishing a new connection identity, adjusting the DNS. While these solutions seemed to work for a while it wasn't long before the problem returned. I have rebooted both the computer and the modem numerous times (it is a DSL connection, BTW). Those actions also seem to help for a while but sometimes they don't help at all.
Since I transferred data from my old Mac Pro I have wondered if I have a preference or permissions issue. I know how to delete preferences when software acts up and that has sometimes been very helpful. But I don't know how to accomplish a similiar fix with the wifi.
Software is up-to-date and I have not encountered any other problems with the iMac.