If you have a site that has a ton of links, there's a good chance you've let a good amount fall between the cracks. When this happens, many times you can generate a large amount of 404 page errors. If you have enough of these you can hurt your rank; turn those errors into 301 redirects with this PageRank Recovery Tool.
http://www.virante.org/seo-tools/pagerank-recovery-tool
http://www.virante.org/seo-tools/pagerank-recovery-tool
