What I can verify tedster is that Page Rank still is the primary factor for the number of URLs which will be indexed and which will stay in the index.
I think this will not change soon. I did extensive testing since the MC stonetemple interview and it's true:
"... the number of pages that we crawl is roughly proportional to your PageRank"
I launched a xx million URLs site which is based on Google Base content, the number of URLs in the index increased up to 1 million, but dropped to about 100K .. the URLs simply do not have enough PR to stay in the main partition or the main index