lammert - 7:11 am on Feb 21, 2010 (gmt 0)

A trigger for manual review seems the most plausible reason for your fall in the SERPs. Requesting links on your submission form, then declining most of the submissions and as latest step nofollow the remaining 2400 outbound links would be a solid reason to remove you from the SERPs if I were a search engine, because you definitely try to game the system.