i have this problem few times but i just reboot the phone and then its okay already. dont know what the cause that make it happen. maybe software bug 

Seems update 8.1 drains my battery quicker but really need few more days to judge

To see what's running in the background, go to your Windows Phone's settings and swipe over to the applications page. There you will find "background tasks" setting at the top of the list.

Once inside the settings, you'll see a list of all the apps running in the background. To shut it down, just tap on the app and tap the "block" button. To confirm that you've shut down the app, press and hold the back button to view any open apps.

EDIT :: Above doesn't seem to work now on 8.1 !!!

go to battery sense app,there you will be able check background app

somehow playing games that are smooth on 8.0 becomes very lag on 8.1

Can't set custom ringtones  Used to love the subtle Facebook pop. Haha

Got few questions thought
-the twitter apps is not funtioning properly..i don't get any notifications from the apps..
-how to activate cortana?already set the language,speech and region to United States but still Cortana wont show up
-why the camera is so..ermm..how should i say it..not exceeding my expectations..i mean even my HTC titan camera is better..i dunno..maybe its me..maybe its the phone

Other than that..this phone is perfect

It appear that only affect user that use bitlocker encryption. I don't use that so should be fine.

does its mean we have to use nokia recovery tools to recover back 8.0 in order to upgrade 8.1?? but i read some where DP8.1 was not able to recovery to 8.0,  correct me if im wrong.

and what's the different between DP8.1 and the official 8.1??

cool comparison, clearly shown the ISO setting would do the trick... all those auto setting sometimes required good engineer to do the good preset setting, and from here we can easily spotted grainy highier ISO when using auto mode... 

for me most of the time when hand held I will go for minimun 1/10 sec shutter speed with lowest possible ISO as any slower shutter my hand simply can't get sharp images... and i believe this number will increase with my age... LOL 

checking on nokia website the update status. india, taiwan show "available" malaysia still testing. hoping they release it fast!

look good. less noise/grainy. thanks! cant wait to receive cyan!

agreed with both you on this. Just a rant here.