g1smd - 12:13 am on Sep 30, 2011 (gmt 0)
I would not use a 302 at all here.
I have recently set 410 for several thousand URLs and 301 for another couple of thousand URLs on a site with a massive duplicate content issue.
It took several months for Google to drop all of the unwanted URLs from the SERPs, but the redirects retained the traffic while those URLs were still listed.
It has taken another couple of months for Google to remove those URLs from the WMT internal links report; only doing so once there are no links found pointing to the pages that no longer exist.
Traffic has increased during this time, even though the number of indexed URLs has dropped by 99%.