There's been a bunch of discussion over on rockclimbing.com about the last speed post, thought I'd post a few things that answered good questions on there:
-We use a single rope not necessarily to save weight (although if you add up the grams/meter it's a close contest), but because it keeps the belays a lot more organized and is generally a lot faster to deal with at transitions. Using two lead ropes invariably turns into a cluster once the ropes get a little icy or the belay is hanging, especially when block leading where the leader is on the "bottom" of the stack. Add in gloves, cold hands, fatigue, etc. etc. and a single lead line is just better when it's better. I use twin ropes, half ropes and single ropes depending on the situation, all have their place. For long relatively fat ice routes without a major approach (more than a few hours) I use a 70 or 80M 9.2 to lead on and a 7.7 (sometimes much thinner, but that gets technical and often isn't worth the hassle either) tag line. The tag line either goes in the second's pack or is towed by the leader or second depending on what's going on...
-A good belay on an ice climb is often one where the belayer can't even see the leader. A cave, a nook, some place that totally protects the belayer from falling ice is essential, and to not establish sheltered belays while leading a block is a crime punishable by free hotel-priced scotch for the second (if he or she isn't in the hospital). An attentive belay is always good, but ice climbing is a very different game than hard rock climbing... On a 70M pitch you're often run five to ten meters between screws, the belayer's main job is to catch a catastrophic fall and not short-rope the leader. There are of course times when every inch counts, and a good team will recognize those situations and respond appropriately.
-I'd generally rather have a belayer using a gri-gri than the other options while he or she is taking a leak, eating a piece of pizza, drinking, finishing a V-thread, and all the other chores that go into being a good team on a long route. I'm comfortable with that, but if you're not then by all means don't do it. Seriously, no sarcasm, you have to know your partner and the situation. Some partner's I'd trust with just an ATC while doing all of the above, some partners I assume I'm soloing even if they are looking at me the whole time. Definitely do use an auto-lock for belaying the second, no reason not to.
-All these points are about making the transitions and climb faster. There are likely safer ways of doing things; four screws at each belay, a screw every two meters on each 70M+ pitch, etc. etc. These transition ideas work great on relatively fat pure ice routes like Polar Circus, Willoughby routes or most Norwegian ice routes.