Why my site would gradually decline? Then crash?

Greetings,

I've launched my site about 10 months ago. 7 months ago I began doing some link building. I would simply go to high quality niche/resource/personal sites and ask them to check out my site and add it to their "cool links/resources/links" page. For every 50 people I ask, I might get 1 link. I built up about 60 high quality links (more than half of them PR3 and PR4) in 7 months, a few each week. Anchor text was varied and niche sites would link to niche main categories in my site (deep linking). More than half the links are deep links.

Every week for 7 months, my rankings for test keywords would slowly decline 1 or 2 positions per week. 2 months ago I submitted a reconsideration request and they said "no manual spam actions found". 1 month ago, my site suddenly lost all rankings and my unique brand name keyword went from #1 with 6 sitelinks down to #20. In addition, the site lost all pagerank on all pages except PR0 on the homepage. Today my brand name ranks at #50. My pages are still indexed, but they don't rank for anything.

I've done nothing but hard, white hat link building. I still receive traffic through direct links and enthusiastic return visitors using my services. I never had good traffic with Google, my best traffic was people searching for my brand name, which is a weird unique name, not even a "money keyword". Now I don't even get my brand name found in Google...

Another odd effect was when my site suddenly lost rankings, a large number of other sites I own in Google Webmaster Tools were also hit with a similar penalty (they still have pagerank though). These sites are unrelated, some aren't even business sites. Not a single one was cross-linked either, many haven't been updated in years so it wasn't a link wheel or a link network.

Does anyone know what might cause this?

Thanks