well the k850 maybe HAD one of the best cameras but in no way can it compete with todays camera phones. the n900 as a phone is a bit lacking but its vast multitude of other features and capabilities more than make up for it.
Not really, it is depending on what sort of work load you running on it though. If you are planing to use it as your Video Player then It won't last more than 4hours. But mp3 player it will last over 12hours. If you are going to use it to browsing Flash contents then it might last 4hours to 6hours depend on what you are running at the same time. So it is quite various, different people got different outcome. So get a spare battery (Original) just in case