I've seen some guides in the Alps and on Rainier put 6-7 people on one rope, with just a few feet between people, and pretty much drag them up and down the mountain caterpillar-style... Do they do the same in the Andes?

It depends on the guide service/mountain, but on Cotopaxi I seriously saw about a dozen people on one rope!

mtvalley wrote:Given a choice between Huayna Potosi + Illimani, or Vallunaraju + Huascaran, which would the South American veterans here choose?

I like the idea of expedition climbing on Huascaran but the normal route is apparently in dangerous condition the last year or so? Then again I've heard about a sometimes impassable bergschrund on Illimani. Which is the better option for moderate but interesting climbs with a reasonable chance of success?

Huayna Potosi and Vallunaraju are both peaks that can be climbed without experience. Success rates are high on both. Which one you'll enjoy most I find hard to say; I enjoyed both climbs, didn't have a view on Huayna Potosi though.

I found Illimani a lot easier than Huascarán, and I would be very surprised if the success rate for Illimani wasn't a lot higher too. Many people don't reach the summit of Huascarán Sur on their first try. I needed two attempts myself, but then I enjoyed climbing Huascarán a whole lot more.

Bolivia was in September 2009. We had no problems with a bergschrund anywhere. I found it a very fine climb, and overall pretty easy, actually.
Huascarán Sur was in August 2011. The route in the icefall is always dangerous; there are many crevasses and you have to pass two dangerous avalanche zones. But it wasn't technically difficult. The crux was higher up: a steep section just below 6300m. Another potential problem: if there is no route above Garganta, finding a way up in darkness can be difficult, unless you have someone with you who has been up there earlier in the season.

Good luck, and let us know how it goes.
Cheers, Rob