I have just managed to get my phone to be upgraded to official Windows Phone 8.1 + Lumia Cyan.. Yay..!! :)
It took more than 30 minutes for the whole process to complete. First, there was update to Windows Phone 8 itself and then it would allow you to upgrade to Windows Phone 8. Overall, the process is very smooth.
However, just after upgrade, I can feel the phone is somewhat slower than before. After ensuring there is no more apps updating, I check on the battery saver that actually all the apps that have option to :"run on background" are now allowed to. I have to go through one by one to turn it off. After that, I can feel the phone back to normal with all the glory of WP 8.1. :)
To go to Battery Saver, just go to Settings > Battery Saver. Swipe to the right to usage, and you can see which apps that are allowed to run on the background. Some apps that are popular to suck all battery juice like Here Drive should be turned off to run on background, and only turn it on when you need to use it.
After choosing background to start screen, transparent live tile on 6" screen really look stunning.