Relationship between 'similar pages' and supplemental?

How to determine why the page went supp & fix

[cameraman]

After straightening out some titles & descriptions, adding a sitemap.xml and simple nav menu, google's site: listing for me went from 3 or 4 pages to 140 and I rose from position 138 to around 67 for what I consider my #1 search phrase. I did these things 4-6 weeks ago and have been waiting around for google to sort it all out.

Of the 140 pages, only 6 were in the main index; all the rest are supplemental. Google 'discovered' my forum - the vast majority of the supp pages are ones it pulled from there, which I don't care about. However, a couple of days ago one of the pages which had actually proudly occupied a spot in the main index disappeared into supplemental, and today another has. The googlebot comes by nearly every day, although they claim they haven't been there since Feb 16 on wm tools.

I tried clicking on "similar page" for the page that went supplemental today, and it only comes back with my main page. The only thing the two have in common is the company name at the top, one image of my product, and the nav menu. Each has enough text to print to just under two pages of 8.5x11 paper (the graphic is only 200x150).

So why did the page go supplemental? Google doesn't have any other copies of it - I looked through all 140 pages. How do I figure out what it is in order to fix it, or do I just sit back and wait some more? I've read the 'hot topic' thread on supp pages and don't see anything that applies - all of my pages are 100% unique content.

I would think that if it's dup content, then 'similar page' would show its "competition", and if 'similar page' means other pages in my site, I would expect to at least see the 5 pages which are still in the main index.

I think they may have misspelled their name - it should be grrrrrgle.