I have iPhone 4S and an iPad2 WiFi both running iOS5.1
I use the iPhone hotspot function to get the iPad on the internett when not at home. This workes great, I had to type inn the WiFi password the first time i connected the iPad, later the iPad connects without having to type the password.
Since iOS 5.1 the iPad sometimes have problems finding the iPhone hotspot. I turn on the "shared internet" function of the iPhone, open the smartcover on the iPad, but it does not connect (the two attached rings does not appear). If I go to Settings>WiFi on the iPad, the iPhone WiFi hotspot does not show up, the iPad just keeps searching. Then after a little while, the iPad suddently connect, ususally after I open Safari or Mail or something on the iPad. If I then close the smartcover, and leave the iPhone hotspot on, reopen the iPad smart cover, again the iPad does not seem to find the WiFi hotspot. I have to turn the hotspot function off/on on the iPhone, and then after a little while it works. When first connected,everything works OK.