My friend Paul Lebowitz, from Wetern Outdoor news and Kayak Fishing Zone,and I did some video this week while experimenting with waders in different configurations.
Waders, wading belt, paddling jacket, and PFD
Waders, wading belt, , and PFD
Waders, and PFD
Waders, wading belt
Waders
and needless to say I did not drown.
These were Hodgman Breathable waders

I also tried paddling pants in different combos
Still did not drown but got a bit wetter.

Bottom line it that the waders were dry and warm when worn properly, even when worn improperly they kept most of the water out.
I would certainly recommend the wading belt and the PFD when ever wearing waders and a PFD at all times when on the water.
Yes this was in a controlled situation in a pool that was 54 degrees. But it did show me a few things about the waders that made me much more comfortable wearing them.

Here is the video
http://youtube.com/watch?v=OYwG52p4yjs

Jim Sammons
La Jolla Kayak Fishing