Here's my experience with them:
Whirlwind: Took it on a 2004 main character. Figured it'd be useful as CC for a empathy/psi defender. It was all right, but because of the drain you'd be better off using it as an emergency escape kind of thing. Also hard to use to herd; too much double knockback and stuff now.
Acrobatics: Taken soooo many times for the knockbackery. I liked supposedly having a mag 1 hold protection on my defenders too, but who knows if that's true? I always preferred it to hover for knockback protection (like on fiery aura tanks and brutes) because of the "follow bug" hover has, where you target an enemy and hit F for follow and follow them... right up until just outside of melee range.
Group Fly: First encountered in 2004 when someone took me flying over Steel Canyon. Oh wait, someone mentioned this scenario in this thread already huh? Yeah that's exactly what happened, too, because he swore he could jump off ahead of me and I'd jump off a second later and pass through the bubble and be saved.
Don't ever believe someone who says that.
Then a few years later I met a bots/FF MM who used it all the freakin' time to great effect. I dig the whole death from above thing.
Group Teleport: Took it on my 3-MM team. Wasn't quite as useful as I thought it'd be, because they were bots, mercs, and thugs (all the ranged types). I took group fly on this group too. I think it'd be best for the zombie and ninja MMs, but are those people still alive?
I have to say though, when in large outdoor missions or even in sewers with a full group, not one person ever remarked or complained when I group teleported us from spawn to spawn. They just grabbed the nearest guy and started punching him. That's the best thank you I've ever gotten for taking a power: Silence!
It was my fault, and I don't blame them for their consistent application of a prescribed moral code.