Keep working on that fear of writing assignments. Lord knows I know as much as any about being swamped by work, etc., but aren't there times in a man's life when he just needs to do something on a lark?
Think of it as bringing beer to a party (or wine, pace, Matthew). Or as your contribution to a great common feast.
The idea of a group assignment is meant to strengthen the group as much as the individual. There's a sense of ownership not only for your particular piece of writing but for the conference as a whole. I think this sense of ownership is wrapped up in a few things:
First, there is a real commitment. You're right - it takes time to follow through on an assignment. But the time spent and the talent spent are a further investment in the conference itself.
Second, there's that sense of a talent shared. How much better off the group is for knowing that each individual member has made the sacrifice - not only to show up for the conference but to say, 'My talent is worth sharing with these other fellows on a common project; one in which we're all looking at the same thing (C.S. Lewis' defintion of friendship fits in here, no?) and expressing what we see through our individual talents."
And lastly there is the sense of contributing to a "feast" of words for both your own and your fellow writers' benefit. The hope is that the work you put into the assigment will edify and further hone your own talent - but it will also be something that your confreres can benefit from as well, on a practical level, as a matter of personal development or somesuch.
Or here's another way of looking at the notion of a group writing assignment: - say you go to basketball camp one summer and althought the other players are all practicing their individual skills (dribbling, lay-ups, jump shots, etc.), when it comes time for a game, each defers. "Nah, I didn't have time to practice before this." "I don't really have the time for a game right now." "I'm way to busy in the summer league I play for to really have time for a game here in camp." That sort of thing. The individuals may benefit, but the group as a whole suffers. There's got to be some give and take, I guess.
It is also a particularly Catholic way to approach the idea of a writer's conference. At least, to the extent that anything that anytime community comes together to witness both a feast and a sacrifice has something Catholic about it...
And besides, on a more mundane level, as we all acknoweldge, the finished product could very well lead to something remarkable - and therefore marketable...
Well, those be my rambling gambols...