To clarify and make it much easier - I would get yourself a battery warning monitor (they can be as cheap as $3) or better yet, get the FrSky voltage monitor for the X8R so you can see/hear when a low voltage point is reached. If you set an alarm for 3.5V (under load) you will then know to land, and the battery will then bounce to 3.7V at rest. That's right where you want to be.
The other thing to wrap your head around - as if there isn't enough already
- is the 80% rule. This is calculated and tracked by watching how many mah your battery takes from the charger to bring it back to full charge. I keep an excel sheet to keep tabs on this - because at a certain point, batteries performance will drop.
For example: your 3300mah battery can be safely used by depleting 2640mah of its charge (3300 * .8). So when you slap it on the charger after a flight, you should be putting back no more than 2640mah, or you have used too much, and have over-discharged the battery. If you discharge too much, you will decrease the performance and lifespan of the battery.
Along with Bart's sticky about Lipos, I've found
THIS site to have great info regarding all thing RC power related.