You did it! Earlier today, somebody on Scienceblogs.com posted the 500,000th comment. It will take a few days for our Seed Overlords to check the counter, contact the winners and make the big announcement. In the meantime, as PZ says, You are encouraged to go on commenting to run the tally up to a million.
And, you can enjoy a randomly rotating selection of cool comments on the Scienceblogs.com front page. I know, I know, nobody ever asked me to fertilize their eggs (not that Mrs.Coturnix would approve), but one of the rotating comments is the historical one here:
PLoS is quite proud of it - you can see this screenshot was already posted in the photo album of the PLoS Facebook group.