Something people need to understand a little with battery life and those nags people get about phones.
First off - Out of the Box Battery Life - I am sure many of you remember that the rep and even some manuals say you should 'charge your battery for 24 hours before using'. This is roughly 'conditioning the battery'. By Law, devices are not suppose to be shipped with the battery installed. And more to the point, the battery is not to be at 'full charge'. The reason for the message of needing to charge the battery for 24 hours is to insure it has a good standing charge and to get the most out of the battery as much as possible.
What most people don't do, and I am also one who has done it with my own droid, is assume that we have a good battery and just use it. Problem is, most batteries do not function in a 'linear' way. Linear meaning, I go 5 steps, it is 5 steps down, I go another 5 steps, it is another 5 steps down.
Most batteries function in a logrhytmic way. Logrhythmic, meaning that I go 5 steps, it will go down 2, I go another 5 steps, it may go down 3, another 5, it may go down to 3.5. It isn't steady or 'straightforward'.
Standby/Talk time - People wonder why there are two different times, and yes, I know many of you know standby means phone isn't being used, and Talk is when it is. What people don't understand is why the battery can't maintain both at the time.
Standby is longer due to the fact that you are not broadcasting. Broadcasting a signal, even with towers trying to receive signals, still takes a reasonable amount of power for a device of its size. The power to just 'listen' for a "Hey, you got a call/text" is minute mostly because you just need to receive a signal and process it. But when talking or making a call, you are not only receiving and processing the signal, but also trying to send out a message back out and hoping another tower will receive and process it. If these were the old Analog phones, the ones with the big battery packs and huge antennas, you would be using a lot more power to do the same thing.
Apps - As many people here have stated, you really don't need to go Kill App crazy, however, you do need to understand something with regards to some apps.
Any app that needs to use the network, will cause a slight drain in the battery. Why? Well, let's explain something about how the internet works.
Network Apps need to 'talk' to something. They send data to a server saying, "Hey, give me data for this..." So now, you are spending a little 'talk time' because your phone is sending a signal out due to that app.
Things like Streaming Music, IM, or even that little weather update app you have running. They will go "Hey, I need more info, send it to me." So you are burning battery power because these chatty programs are sending data out to get more data in.
This is the reason why one of the battery conservation suggestions from the droid booklet says to not have background data or sync on all the time. While Gmail can push its mail, the pop/imap stuff will require you to setup a time interval so you can get your mail, but generally, you want it at a longer time interval to avoid constant 'chatter'.
And just so you know, IM is one of those constant chatter apps because it does ping the IM Server with the "I'm online" status. Most IM programs don't have a convenient 'sync' timer to do that, as IM servers and clients like to keep 'up to date' on status for that reason.
This is not to say you need to go crazy or OCD on killing tasks, just be aware that if you want to prolong your battery life, make sure you minimize the number of network talking apps as much as possible. The fewer there are, the less 'talk time' is used on the battery charge.