I think the assignment itself worked out really well, offering possible research sources for their upcoming essay, modeling how to analyze and evaluate a source, etc., and most students did impressive work. But, some have not done their assignments. Normally this would only affect that student's grade but pairing them the way I did means that some students cannot do their homework until other students post theirs.
I resolved this temporarily by letting students switch their paired groups to one whose work is complete. And, of course, this can happen with live peer review, too. How many times have I carefully crafted student groups only to have absence, lateness, and/or unpreparedness interfere? In a way, doing this online makes it easier in that they have the whole weekend to post their work, not just a one- or two-hour class session. Also, students can look around at what other groups are doing and I was able to switch groups fairly easily. But, it's been a bit clunky and I would welcome suggestions for future implementation of this sort of assignment.