Is there an official list of the largest sites running RoR?

Our site is growing fast & the last few weeks, we've been running into
a few scalability issues. For reference, this month we're generating
more than 600,000 unique visitors, and on a given day, we get an
average of 350K unique requests between robots, users, pageviews,
stylesheets, etc.

The site is all running on one webserver, which runs apache, mongrel,
and posgressql. I know we're not the "biggest" site out there running
RoR, but it seems like we have to be in the top 10-20. Is there an
official list of the largest sites running RoR? The reason I'd like to
know is for example, the guys at 43things post a bunch of technical
info, same with the revolution on rails blogs, both of which are huge
contributors to the community & my own understanding (I'm the
marketing / product guy, not the technical wizard).

If you know of any good lists like this, or can send them to me, I'd
really appreciate it. Thanks!

There's not much out there, but twitter.com is probably the biggest in
terms of hard usage (11,000 requests per second). Shopify.com is
pretty big too, and they have been quite clever with some monster
caching server (RAM in the Terabyte range for their cache server, and
about 99% cache hits).