My group is using a homebrew assignment submission system, but is planning to move to the Moodle Assignment module. The only problem is that the module doesn't have a facility for students to request a deadline extension - yet. I plan on modifying the Assignment module to implement this as part of a JISC-funded project
So, before I get too stuck in, I wanted to say Hi! and ask for any thoughts on the area, as I want to submit it back for inclusion in Moodle core.
Here's the only thread I could find on the topic: http://moodle.org/mod/forum/discuss.php?d=5915 which has a few interesting points.
I'm just starting the project, so don't have much more than a broad plan of attack, and a desire to track Moodle source via the Catalyst Git import (see http://docs.moodle.org/en/Development:Tracking_Moodle_CVS_with_git).