I've got a Powercore (plus warious Waldorf and Acess 3rd party plug ins)
There's a few memory problems with the Powercore but it seems that when you add a Ti it becomes a world of pain, a good friend sold their Ti because of the grief...
and it too works fine with Live on my system- the Virus Ti seems to cause a lot of people a lot of problems (in particular a Mr Rei Loci of Iridite who hasn't been able to get much out of his since getting it a couple of months ago- Cubase SX user)- not saying that Live is completely flawless but I would say its the most well implemented piece of software I've used since Notator in the early 90's
I have no problems at all with 4.1.4 but five has been a pain where midi has been concerned. Dropping notes, holding notes and switching patches - and if you do a long jam session the whole thing starts to lose sync...
M