Thanks for all the feedback - overwhelmingly good (so far), which is nice. We noticed a couple of things as users started actually hitting the system which we believe we've tweaked successfully. We've certainly turbocharged the database queries, which turned out to be our main resource issue.

This afternoon we've made another major change. We've put Twistd on port 80 and removed our reliance on Squid. We did this to tackle the occasional timeouts, but also to decrease the complexity of our install (we've also removed our reliance on DivMod's excellent Mantissa as we realised that it was unnecessarily complex for our needs). This means that there may be some oddities - we have a feeling it should go quicker (and it's definitely simpler under the hood), but if you see anything odd please let us know by leaving a comment here.