OK - I know most people are like really pi**ed off by how quickly the phone's juice gets drained and how the iPhone doesn't require such stuff like Advanced Task Killer or whatnot to maintain the battery usage and I completely agree. It will take you a minimum of 3 days to get the battery to a more acceptable level but after 2 complete weeks, the battery life should run for a satisfying amount of time. People say completely letting the battery die and then recharging it every month or so helps. I wouldn't say so - and dont do it frequently if you have plans of doing so cause the type of battery inside will die. I agree - we paid to use the phone for such vigorous tasks and it will just completely destory the whole point of owning such a powerful phone if we cant use it to the max so dont worry. It will take 4 charges or so for it to really get the hang of things. I recommend you set the syncing to manual so you can find out when you want to since this saves up a lot. People really dont need the weather so remove the widget if your not gonna use it - dont use animated screens cause they do use up some battery but not an awful lot - its advised you turn it off if your low on juice. Dont multitask unneccessarilly, like dont keep stuff running when your probably not gonna use it. Turn off wifi when not in McDonalds or your house (or if you do live in McDonalds) - only turn on 3G when you need to surf the net. Get rid of Friendstream - it takes a lot of life!!
You should easily get 17 hours or so out of your battery by then with moderate usage (half hour of calls, 100 texts, an hour of surfing, half hour of messing about with apps). I think thats fairly good - just let your device charge overnight. I really dont see why people are complaining. Even 10 hours of battery is enough cause I really doubt you'd have much use for a phone like the Desire when your at home - I'd only expect one to carry it around when out and about. Just let it charge whenever your at home if your gonna heavily use it. This is the sort of length you get out of any touchscreen (Androids and iPhones).
I do warn people though - if you plan to get FroYo, dont be in any hurry cause many have noticed a decrease in battery life ever since they updated it (including myself). I get around 6 hours with FroYo on :S
Dunno if thats just me but others have complained about the new update too.