I don't own breathable waders but afer reading the posts it sounds like I ought to ditch the Cabela's 5mm bootfoots for all but the cold weather drift boat steelheading.
I fish in Alaska and would like to re-iterate the good advice in respect of layering. For Alaska I start out with polyproplyene long handles (THESE ARE A MUST. DO NOT WEAR ANYTHING ELSE.) Over them I wear 1-2 pairs of wick-away ski pants, THEN put on the 5mm waders. (I've walked up to 5 miles in this get-up, I can tell you that I was HOT when I finally reached the river!)
More frequently, though, a very long day in a boat or a 38 degree river can get put a chill in you if there's even 1 non-synthetic item under your waders. I learned the hard way: no cotton sweats, no jeans, no traditional long handles.
This goes doubly for SOCKS. I recommend trying either 'Sealskins' or Cabela's Gortex socks. Both are spendy at $30-35/ pair. However, if you want warm feet you need something to wick away the sweat and neither cotton nor wool does the job like these.
I've used the Gortex socks longer and they've held up well but you have to take care when putting them on as there's no elastic in them and they can be torn. The Sealskins worked a charm the one week I wore them last fall, and have the added advantage of being stretchy.