First of all, what's the point? In my experience, *if* you pull aggro on a boss, 5 secs to fade is too long and the boss ends up hitting you anyways. Then you either die or the invisibility fades, neither of which are helpful. Ice Block is the only thing I use when I grab aggro. And if I want to stop generating aggro, I just stop casting. That works well enough that I don't need to pop invisibility.
I mean, it's useful in some soloing situations and it's fun to play around with, but other than that I don't really see any use for it.
Am I missing something? Or is Invisibility kinda pointless in raid situations?