Yes, that is tail whipping, Trapt. Tail whipping is also very useful for stunting people's recover. Tail whip them when they try to recover, they won't bounce up, like they do with the PKT Head, and will stall in the air.
Also, I use tail whipping the majority of the time I attack with PK thunder. It's just so useful. You can circle the opponent with a tail whip to rack up quick double-digit sized damage. And, the tail whip is good if the opponent is in the air (not recommended to take your PK thunder too high into the air because if it misses, you're stuck vulnerable) because if you guide your PK thunder right, such as following their decent, you can tail whip them even if they airdodge because the tail is quite long in Brawl.
Tail whips usually lead to a free PKTHead to the face or a PKT2/PK Missle/PK Rocket. haha. [:
Oh, and don't forget that you can ground your PKThunder if you find out you don't need it anymore, hopefully you'll rid yourself of it's lag before your opponent and remain unpunished. Or, you can even hit yourself vertically (on the floor) on the head with your own PKT to keep safe. It'll slam you into the floor with no damage taken, but you have the chance to use an invulnerable get-up move which is always nice; such as the kick or a roll to the side when they approach. All in all, just practice, practice, practice and experiment with PK Thunder. It's such a ridiculously useful move for Ness when used to its fullest potential; essential.
I hope I helped a little, Trapt.
Earthbound, have you been able to use the reverse edgeguard by sending the thunder in front and below you and back around for a diagonal down PKT2 to any effect? It's really handy with Lucas but I'm not using Ness much anymore so I don't know how practical it is for him.
Tyr_03, I hope you don't mind me replying to this, because I'm obviously not EB. But yeah, I've used it some times. It doesn't seem to work as much as I'd like it to anymore but that might just be because I attempted enough. Well, because of the floaty mechanics, I've even been able to reverse edge guard with an angle of PKT2 that actually goes away from the edge, land the hit (because they might try to airstall, the reverse angle helps pretty well), and still make it on land [: It's scary but I think it'll be worth practicing because it's easier to recover from now [: