Upgrade requires 3.7 GB free space, had to sacrifice some of the installed apps temporarily to make room.
Installation took close to an hour. It retained all my settings including wifi settings etc (as usual). The UI will take some time to get used to, large animations kind of on your face type.
There is a noticeable lag compare to ios 6 in iphone 4, I assume it is mainly due to the added animations. The control center is very useful! You can enable or disable wifi, bluetooth from there. Control center is accessible even when the phone is locked. It also got a torch function.
Couple of new sounds added for ringtone and alerts, i liked it. No Siri :(, camera mode allows you to add filters before you post or share it.
Overall I am happy with the upgrade, it seems to have added a fresh look to my three year old iphone :)
Btw iOS 7 supports per app vpn and sso across applications, interesting from an enterprise and usability perspective.
