i have the same problem with mine iPad2.
I had the problem already at iOS4.x and hoped that the problem would by over after the update to iOS5. But no.
1. sometimes i get: NO WIFI (mostly gone after a hard reset),
2. sometimes the ipad don't find any routers (not at home, work or anywhere),
3. sometimes he find a router, but cannot connect,
4. and suddenly i have a couple of seconds, or several houres of connection.
There is for me no explanation what's going on.
I tried every answers on forums and i don't know what to do. I love the iPad but it ***** when you dont't have any wifi.
I hope that Apple comes with a answer.