Hallelujah
By way of update, I solved the problem. Having already changed from wep to wpa2 and doing the restart thing for iPad and router, etc--and it still didn't solve the dropping, I turned off "auto" brightness. For some reason, that did the trick. I got no info from this forum at all, and it seems Apple's official stance is to say this problem only affects a very few and so not much on it; but the tip for the brightness control I got from some official Apple address to the problem, I can't remember where. Anyway, problem over. deanxxi
Having looked for days of this problem, I read about the changing firmware which is always being suggested and never actually do anything, whether it is for the iPad or computer. I see even in this post someone is suggesting iOS 6 is supposed to fix it, which of course it won't. as nobody seems to know the source of the problem, how can the newi iOS fix it. Even changing the router, which would be my next step, does not make sense, as all my other units work well on the wifi. Anyway, i was getting very annoyed, both at the problem, but also at the standardised suggestions, and finally very pleased to see that the auto brightness fixed it.
True, it still disconnects, but at least now it also reconnects so it is as good as it can get. Don't listen to the people who say it doesn't work, as it fixed this problem for me, when nothing else did. (reset network, reboot, renew, forget,etc). If your router don't work, or your network settings are wrong, of course it might be this causing the problem, but for the iPad continually disconnecting from the wifi without reconnecting, the auto brightness off setting fixes it. Thanks, iPad 3iOS 5.1 (jb)