Nice article on Axon Flux about scaling a Rails site. Some helpful tips on monitoring processes and queries, using S3, search engines, and how so many Rails articles and plugins get out of date so quickly. I guess the article is more of a "helpful tips" post. But it was still handy.

Incidentally, New Relic looks really nice. I assume it's not totally free, or else a paid version will come out soon enough (a la Hoptoad, which I liked before & lost interest in).