Here is a great presentation given by Jason Yan and David Cramer of Disqus fame about how their site was architected in order to scale to handle 75 million comments.
DjangoCon 2010 Scaling Disqus
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Home on the Digital Range
Here is a great presentation given by Jason Yan and David Cramer of Disqus fame about how their site was architected in order to scale to handle 75 million comments.