In reply to Bluebird:
Like others, I've used Sealskinz for running and mountain biking in really wet conditions, but not sure I'd want to for walking. My feet do feel clammy in them, but this is better than soaking wet. For a run, the duration is short for me, so slight clamminess is far better than soaking wet, and for a bike ride, the feet don't seem to sweat as much. More importantly, they stay warm, even if slightly damp, whereas the next cold puddle would make them cold again with normal socks.
Over a long day walking, I think the poorer fit than normal socks, and reduced breathability, would make my feet less comfortable than normal socks.
Note that if you run or bike in them in shorts, the rain can come down the top!