Here are my theories so far:
I beleive a combination of issues is causing some of these battery issues, rather than one specific issue. The following are my observations and theories I ahve formed after having spent time using the Lumia 800:
+ I think there is a bug where the phone gets caught up in some kind of loop and starts to consume processor capacity - this results in a rapid drop of battery power over a short space of time. This coincides with the handset becoming warm or hot, even if left away from a heatsource.
+ I think there is a bug where background tasks are allowed to carry out too much activity, even when not connected to WiFi - this results in the phone being quite busy, and battery power suffers. This would explain why users who say they have 'backed out' of all their applications see less of a problem.
+ There is a bug where WiFi fails. This manifests as the handset not connecting to a known WiFi network, and when you access the 'settings' - you cannot go into the WiFi section. At the same time battery life plunges. This could be the phone repeatedly trying to reset it's WiFi stack.
+ I think there is an issue with the way the phone monitors the battery power, which affects both regulation of charging and discharging of the battery.
+ I think there is an issue with the way Live Tiles are handled - some users have reported improvements when they have reduced the number of live tiles pinned ... including removing the 'People' hub Tile.
These are just my observations, and there are other theories out there too.
One thing is clear - even if you can improve the situation by turning off this or that, you certainly should not have to - and some of the issues that are affecting the handset are clearly bugs or faults, and Nokia need to come clean about that, particularly if it's a physical issue that can't be addressed with a simple update.