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I wonder if its a glitch, proactive (google checking "suspicious" sites) or just google acting on "spam" /other complaints.
Also, could the number of pages on the site have led to a a manual review? With the flood of huge computer-generated sites these days, Google may be looking more closely at a database-driven site of 110,000-120,000 pages than it would have done in the past.
It is not happening overnight... The site is active since 2002 November. Considering that we have close to 100,000 members (not bought databases as many other sites, they all registered) that submit their own content (many site sections), 110 - 120 thousands of pages is not a lot at all. It is a business portal used by thousands of companies.
In other words, it's taken a little more than 2-1/2 months for PageRank to display on the new index.html page. I don't know if that's typical, but it's nice to have confirmation that the page isn't lost in space.