I'm having similar issues too.
When I was on vacation recently at Phuket, I was attempting to login to the hotel's free wifi. As what Dan said, after selecting the SSID from the list of wifi spots; there is a Safari page that will require you to login with some credentials. Sometimes this takes a while, sometimes it is faster.
As I said, my recent trip, I am able to key in the username/password, but when I click on "connect" or "login"; nothing happens. Even when I wait for, like, 20 minutes to see if anything comes up; nothing.
Hence, I thought it might be an issue with the hotel's free wifi (note that at this point in time, both my iP4 and iP3GS have no issues logging on in the same way).
Just today, I tried logging into the free wifi at our community library, again the same thing happened. Both iPhones are able to log on. But iPad - after keying in username/password and clicking on "connect" results in nothing.
Any idea what might be the cause? I can logon to my home wifi (thank GOD!). But from time-to-time, I face the issue of the iPad telling me, "Unable to join [SSID]".
Is it likely a hard-ware issue?
Thanks.