Since they had to share the file with me, getting access to the presentation on the day was easy and, even if other students were absent, the rest of the group could still do their presentation. The "John did the Powerpoint, and he's away today so we can't do our presentation" excuse was no longer applicable.
I also asked students to be involved in assessing their peers using Google Forms. It included a couple of compulsory questions like their name and the stage they were assessing. I like to include names so that I don't get silly comments and votes.
This was pretty simple scheme and seemed to work well. I toyed with the idea of getting them to make comments but on reflection it would have taken too long - especially by the eighth presentation.
Finally, I could go to the 'responses' page for this form and use the 'average' formula (see results in red below) to get an overview of what students thought about their peers. Hence the need to use the 1-5 rating scale. Mostly the student rating was similar to my own (blue rating below) which was interesting.
This all depends on getting one-to-one access to computers but I would regard it as a very successful series of lessons which promoted collaboration and peer assessment to a high level.