Mittens and twist shifters rule!
Specifically, SRAM XO twist shifters. I've had twist shifters in the past, in non-winter riding conditions. The lower end ones kinda sucked. But the higher end units shift as good or better than any triggers. Using the XO's this winter made it easier for me to take advantage of the best cold hand solution, mittens rather than gloves.
They have worked perfectly, much better than the Deore and Rocket triggers I had before. But the greatest benefit has been being able to use a $10 pair of ragwool insulated gloves inside a larger sized $10 mitten shells.
So if you're a winter commuter who has cold hand problems with gloves, I'd really recommend these shifters.
Long Distance Cyclist
Mittens rule ... I use mittens with my STI shifters quite successfully.