I've read some great advice from the folks in this thread regarding the techniques used to preserve battery life, one of the most useful is of course the Power Widget...
Also, I would suggets d-loading the Advanced Task Mangaer app, it allows you to quickly view all apps that are running, turn off what you do not want/need on, as well as quickly delete any apps you no longer want on the device.
As to the charging overnight thing: as a Verizon employee, I have from time to time had people come into the store complaining about their battery not holding a charge (this is for all phones, not just smartphones) on a device that they have had for only 6 months to one year...the 1st thing I do is take out the battery and attempt to spin it on the counter, and if it spins, it is swelled, which usually means it has been overcharged.
I then ask the customer if they have been charging the phone overnight, and the answer is always 'yes'.
I have read through just about every users manual on damn near every device, and have never come across one that states there is a 'auto shut down' in regards to charging on the phones..I had one tech tell me that Blackberry's have a 'trickle mode' when the batter reaches full charge and is still connected to the charger, but I never found that info anywhere.
If someone has come across info that says otherwise please share it, however in the meantime, I would suggest not charging a phone overnight.