I had a strange situation yesterday which caused me to restore the phone back to iOS 5 b6 with a backup from several days earlier.
I noticed the pesky usage = standby issue again yesterday. In the past, doing a hard reset fixed it... but this time I decided to explore a bit. So I shut the phone off and waited about 30 minutes. I powered the phone back on, and made a call and sent a couple of texts, then set my phone down on my desk. After about an hour I picked it up to check Twitter and discovered that it had shut off again. Next, I powered it back on and attempted to use the phone - and ALL apps except the native Apple/iOS apps (text, mail, phones, maps, etc) flashed open and then crashed back to the home screen. Nothing that I did would cause the phone to respond correctly, including doing a hard reset.
I hooked it up to my MacBook and tried to sync - it went through the motions, but nothing actually synched... so I chose to restore to iOS 5 b6 and then restored from back up that was 2 days old. GRRRR.
A day later, no issues are evident...