As with ANYTHING, you will get contradictory information. Early on in the LiPoly revolution, 2.5 Volts per cell was considered to be the minimum voltage to which you could safely draw your LiPoly packs. This was found to be untrue. While you could get away with it MOST of the time, the extra stress put on the batteries caused some cells to become damaged, leading to unbalanced packs, overcharged cells, and battery fires.

With this experience, the limit was raised to 3.0 Volts per cell. Since then, the number of fires and problems with LiPolys seems to have steadily decreased, even though LiPoly use has grown by leaps and bounds.

The 3.0 Volt per cell limit is actually a hard limit. The cell should never go below 3.0 Volts, whether sitting idle or under full load. If you have to reduce the cutoff voltage to get decent flight times, you're overstressing the battery, and asking for trouble. Get a more capable battery, or reduce the load on the existing battery.