reference: see the text on familarity heuristic. every body do it, so it most be true... not always true.
Everything old is new again. Again, we're talking about heuristic clues. Maybe I should bring up ethics and norms just for good measure.
When I go ice climbing, I bring a cotton t-shirt. I leave it in the car with a full nalgene and change in to it right before I hydrate.
I carry two synthetic base layers: I change from my soaked one in to a dry one at the base of the route, after the long hike in. Yes: I go down to bare skin in freezing temps, but only once, and only at the part of the trip where I am likely to be warmest (after hiking miles uphill with a heavy pack).
As was mentioned before in this thread: the best way to carry a lighter load into the backcountry is to lose weight. If you can lose ten pounds and still be healthy, you can carry an extra t-shirt or two, cotton or otherwise. If you are already in peak shape and are trying to shave weight, I'd steal some hints from the ultralight-backpacker movement. Start with the Ray Jardine site: (remember the guy who invented SLCDs?) http://www.rayjardine.com/index.shtml
Some things the crazies who practice ultralight backpacking do that might be useful:
1. Don't take a multitool, take a razor blade.
2. Lighten up your medical kit.
3. Take everything out of the original containers and use lightweight baggies or small stuff sacks.
4. Trade your heavy fleece hat for the lightest warm one you can find. I wear the Mountain Gear windstopper one that weighs almost nothing.
When you get back from a climbing trip, dump your pack on the ground in your shop and sort your gear in to piles: 1) stuff you used 2) stuff you didn't use and 3) stuff you didn't use, but is emergency gear that you're taking next time no matter what. Then make some decisions.
I think LL's take on cotton is strange: but it looks like he's thought it through and developed the technique over a long period of time. I am glad to see he warned people off of it as not recommended. Please don't haul 10 cotton t-shirts around in winter and change them every couple hours unless you really understand what you're doing. However, I agree with LL on one point: leaving gear behind to shave weight on winter trips is risky. Much better to shave weight from your body if you can.