Some good views and counter views. I guess it comes down to "fitness for purpose".
the points made in the quote below got me thinking about one and prompted me to create this thread on a kayaking forum. Why? seakayakers are gear freaks and I was certain that something would be reccommended. Thanks for heads up on the Kokatat SeaO2, patrick. I've added the link to my favourites should I decide to go down this path.

"Why does everyone rate pfd's so highly. They are not lifejackets, they are merely designed to help you float better. If you are unconcious or hypothermic you will drown anyway because there is no neck support, your noggin will simply flop forward into the water and unless someone pulls you out your stuffed anyway. My personal opinion is self inlators are a heaps better option because
a) they're cheaper
b) easier to wear and heaps more comfortable than a PFD
c) easier to remount in one
d) less hot to wear
e) have whistles and mirrors and pockets for flares
f) can still swim and duckdive waves in one
g) if shit happens you pull the cord and you have a REAL lifejacket with neck
support designed to float you on your back if you're buggered.
Peronally I only wear it if I'm paddling away from the beach or in dodgy conditions
but it is a whole lot more practical than my PFD and therefore I am more inclined to use it"

The only point that i disagree with is a)"they're cheaper. Sure they are cheaper than a marathon paddling PFD but they are more expensive than a standard kayaking PFD.