Cash, I would gladly start such tutorial :) In fact, this is a good start already. I think the most valuable data would come from Curverider though, as I suppose you have the most experience with scaling really large sites. I can write tutorial eg. on optimizing Memchache, but my experience with optimizing Elgg are limited to websites with max of 15k users. Elgg.org has 40k users, Brighton community has 70k users, I suppose there are websites even bigger than them.

I think it would be a really great aid for new users if you could share experience from hosting those sites in some form of a case study.

I suppose this is too complex question for an "ask Elgg" feature though :)

try this, it's not much but it's something: http://websiteoptimization.com/services/analyze/

Y'all welcome to PM us re: FBFK @ ~174K userBase