Rebirth - With a negative energy swap, this skill can be used it battle without draining your energy, but should only be done in VERY careful circumstances. This being said, 99% of the time you see someone mid-rebirth in battle (in a PuG), it's a bad choice.
qft
The only time it is acceptable, IMO, is when used by a mesmer with enough fast casting to make it significantly faster to cast. Then you also have to make sure to res the person outside the range of the fight so that they don't just get themselves beat right back down (if you start running away from the fight right after the animation that brings them back to life starts, you can pull them a little farther away). The only reason this is acceptable is that the skill also helps for near wipes as well, and only then if used where res shrines aren't available.
Anyway, there are almost always better options...
The only time it is acceptable, IMO, is when used by a mesmer with enough fast casting to make it significantly faster to cast. Then you also have to make sure to res the person outside the range of the fight so that they don't just get themselves beat right back down (if you start running away from the fight right after the animation that brings them back to life starts, you can pull them a little farther away). The only reason this is acceptable is that the skill also helps for near wipes as well, and only then if used where res shrines aren't available.
Anyway, there are almost always better options...

. Half the time it's a waste of a slot and a sig is only good once. In my PuG experience, if a rez sig chances are they'll never get enough moral to recharge it. It also means everyone is likely to get slaughtered in short order anyway because they are being careless.
