The problem was probably caused because there was a huge rush on the OTA downloads as well as iTunes and the latest iTunes update so the servers probably couldn't cope.
@ukdolfan the reason for the rush into updating is because of the battery draining issues plagueing the 4S and 4 on 5.0.1 but to be honest its not massively improved it
"I doubt very seriously this would happening if Steve Jobs were still alive."
Yeah, because everyone knows that Steve Jobs was a supercomputer that could handle the internet traffic of 500 million iphones simultaneously downloading the same program.
You, sir, are a turd and I hope Steve Jobs haunts your pets.
If you are getting the error message "Unable to check for update" when you try an OTA (over the air update)
Change DNS Servers
Settings -> Wi-Fi
Click the blue arrow on your connected network
Delete everything in DNS and replace it with 126.96.36.199, 188.8.131.52
If this works, you will probably want to remove the WiFi network using "Forget This Network" and then reconnect to it to get your original DNS servers back. Alternatively, make a note of the original DNS servers before deleting them and replace it after you are done.
If you are getting the error message "Unable to check for update" when you try through iTunes
On your Mac
Choose Apple menu > System Preferences, and then click Network.
Select the network connection service you want to use (such as Wi-Fi or Ethernet, unless you named it something else) from the list, and then click Advanced.
Click DNS, and then click Add at the bottom of the DNS Servers list. Enter the IPv4 address for the DNS server.
You can use OpenDNS
You can Google Public DNS if you want
Hi, Been having the exact same problem, have 4 devices that can upgrade to the new 5.1, it dosent matter how you go about it it just will not update, I was on the phone to apple again today as I have been trying to update for the past couple of days, they suggested resetting my router (techs always say that first) but they really did not have any answers, I also tried downloading direct from apple the software update is there on their own website but there is no download link, also third party link like redmond pie points to direct apple download but the page just hangs. When I pointed this out to apple they didnt know what to say! I use the ipad a lot and wanted to download the new iphoto app but seeing as I can not get the update I cant buy, I dont like the notion of everbody is trying to update all at once, apple know how many devices are active, what software is currently being run and I am sure that they would take a lot more flack if the servers kept on crashing, but why is there no direct link to the download for 5.1 on their own website?
Agreed most of the time. However, some of my app's on my devices are in need of updating with the 5.1 and are hung up. So, we either need an option to quit the updates of the app's or we need an announcement from Apple to discuss what is going on for their faithful customers. Apple's PR folks need to emplore the company to speak up! I'm just sayin'....
finally managed to update, changed the dns settings and then it worked, ipad however a bit buggy, also thought that dictation would be on there but got left behind again, really could have used that feature, I will wait for ipad 4, like i have done and waiting on iphone 5, cant keep up with updating my equipment every time a new one comes out, anyway i tried the dns settings 184.108.40.206 and it worked used one of the redmond pie links to get the 5.1 software