I picked up the 303's this year in a wide. I only got in a few rides, but one was the Town Run nite-ride which was probably 15 degrees. With a blaze wool sock (no warmers) my feet felt good for an hour and a half with the occasional hike through deep snow. Only problem I'm running into is I get rub against the crank, but my summer shoes do this to a small degree (even with cleats moved all the way inside).
I prefer arch support which is lacking, so I plan to take out the insulated footbed (appears to have air pockets and aluminum foil) and replace it with a Specialized arch support. Hopefully this doesn't off-set the warmth too much.
I can see them being very handy for commuting or long rides where neoprene covers would get wet.
Also, the BOA system made me regret not paying for this feature on my other shoes. It's very nice.