I snuck up on a guy and was about to assassinate him when he turned around at the last second and stuck me as I hit him. He backpedaled while I sprinted toward him and he used thruster pack to go backward right before the grenade blew. He was still very close to me.
Apparently it's good for temporary invincibility to plasma grenades... --- Halo 1 LAN vid: http://www.youtube.com/watch?v=VhjWnJU2EKY Number of times Killean_Nuggets has invalidated someone's post based solely on their Halo skill: 7
It's situational, and the situations tend to be things that can be avoided if you are more cautious, or if you use other AA's. Turn a corner, and see something you don't like? Thruster Pack. At the same time you could have just used PV and seen that you shouldn't turn that corner. Vehicle trying to run you over from the rear? Thruster Pack at the last minute to avoid it. At the same time you could have just payed more attention at the radar and jumped without it nearly killing you. That's just two examples, but you can see what I mean.
With that said, I still love Thruster Pack and it's my go to AA. It is situational, but I tend to get myself into situations that tend to take advantage of it.