when should I charge my iPhone battery? Should I wait till the battery is all the way drained? What's the best way to keep battery life?

There have been a lot of posts about this on the Apple Discussion pages (http://discussions.apple.com/category.jspa?categoryID=201 ) and elsewhere on the net. These batteries reportedly do NOT like to be run down below 20%. Here is Apple's official page: http://docs.info.apple.com/article.html?artnum=305742

FYI - AppleCare for the iPhone is out now; it will add one year additional warranty to the original purchase warranty (including battery coberage) for $69.00
http://store.apple.com/1-800-MY-APPLE/WebObjects/AppleStore.woa/wa/RSLID?mco=19D94099&nplm;=MB135LL/A

http://www.apple.com/batteries/iphone.html

Seems to be the official word from Apple.

lithium ion batteries should be drained before recharging or they develop a "memory" which will shorten the life of the battery.

I think not gooch. I the case of iPhone and new notebook batteries, they do not benefit for draining completely and recharging.

1) A new battery usually maintains a discharged condition with very low capacity. It is highly recommended to fully charge new battery packs before using. You can refer to the users’ guide of your electronic device for charging instructions.
2) A new battery pack needs to be circled (fully discharged and recharged) three to five times to reach its optimum performance.
3) Rechargeable battery will undergo self-discharging when left unused for a long period of time. Thus, it should always be stored in a fully charged state and kept in a cool, dry and clean place.
4) To maintain the optimum performance of a battery pack, it is highly recommended to circle (fully discharging and recharging) it at least once a month.
5) It is normal if a new battery gets warm when being charged or used. However, please pay special attention if the battery pack becomes excessively hot. This may indicate there is a problem with the charging circuit of the electronic device. Please consult a qualified technician if necessary.
6) New batteries are hard to be charged. Sometimes, your electronic device may indicate a fully charged condition about 10 to 15 minutes when the new battery pack is being charged for the first time. When this happens, remove the battery pack and let it cool down for about 10 to 15 minutes then repeat the charging procedure. Sometimes, a new battery will suddenly refuse to be charged. If this happens, a suggested solution is trying to remove the battery from the device and insert it again.

detail:
http://www.lithium-batteries.net
http://www.my-batteries.co.uk
http://www.canada-battery.ca