two-person winter quilts?

Well it's feasible, Nunatak makes a dual Arc Alpinist:

http://www.nunatakusa.com/site07/arc_products/arc_alpinist_dual.htm

Sounds miserable to me. I wouldn't bring anything but a -20 or below bag out. A quilt would have cold spots and need a super good pad and like 7 inches of loft for me to even consider it. Plus a double bivy sack.

Definitely feasible

http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/11371/index.html?

I can help with more details if needed.

Jacks'r'better make their family of large quilts for 2 people. We (my other half and I) have a Mt. Rogers and a Katahdin. We can use one of them for a 3 season quily; use them individually as bags; join them together as one big bag; or drape both over use for one very warm but still light quilt (with good mats under us of course). It's a very flexible arrangement. The Katahdin is the loftiest at 3.5in.

Worth checking them out, imho.

Have you guys seen the video on Patagonia's website where Steve House shows off his two person quilt for the alpine?
It looks great, I think I'll post in the MYOG forum re: that.
Cheers, Rob

My wife and I have some summer Pertex bags/quilts with 300 g of 800 loft down in each one (MYOG department). We have used them as quilts down to -7 C layered on top of each other, but that only works for couples!

For winter use in the snow we take the same summer bags and a Pertex quilt about 1.6 m wide with 600 g of 800 loft down, to go over the top of the summer bags. Works great – sometimes the quilt gets a bit damp from condensation etc, but the 'inner' bags stay completely dry. Plenty warm.

Just back from the snow with that combination (it's winter here now).

Cheers