I'm having a different, but related, problem to the one Steve just posted.
Every week or so, my students have 2-part (posting/ reading + commenting) assignments like:
a) post your blog by Sat. at Midnight;
b) respond to your group of 3-4 'partner' peers' blogs by Monday night.
However,students often fail to meet deadlines like these (for all their long-standing and variously weak reasons plus new technology-based excuses such as "my computer exploded" or "I can only use a computer once a week"). Once this hits critical mass, as it has in some groups where one very diligent student is entirely abandoned by his/her 3-4 tardy-to-noncompliant peers, this basically ruins the system. Since it no longer rewards those who do follow the rules (they get no feedback from peers and feel anxious that their peers have no work for them to comment on), its kind of demoralizing.
I have lost control of the system for several reasons:
1) I am too preoccupied with having a private life over the weekend (albeit one filled with paper grading) to monitor each of the students blogs and posts.
2) I have been too anxious to harshly penalize those who may truly have technology-access or technology-knowledge issues that keep them from satisfying these assignments. This was especially true in the first weeks, and I feel this initial leniency 'set the stage' for wiggly deadlines and a less-than-effective reward/penalty system.
I have just announced new stricter grading, but I'm afraid it will result in a bloodshed of lowered grades rather than improved results.