tedster - 7:34 pm on Dec 7, 2010 (gmt 0)
Unique meta descriptions used to be very important for getting more pages in the main index - but that was before Caffeine was deployed. I haven't tested it since then - but my sense of it is things have shifted.
I do think it would be better not to have any meta descriptions at all than to serve a whole lot of duplicates. But especially at the scale you are describing, you're probably much better off the actually write unique descriptions. It's not that big a job, just big enough to be a bit of a PITA.