There's a direct correlation between the "Online Users" value you see on
the main page and how responsive the site is. Our dual-Xeon E5410 server just can't handle the CPU load during peak hours (evening time in Japan.) Still... count your blessings. The fact that we can even post when there are 5,000 online users is thanks to a huge bevy of performance tweaks added in the past year.
Apparently our datacenter is going to start offering somewhat more powerful CPU options (dual Opteron 6128) for their high-end servers. If they do, I'm sure we'll upgrade ASAP.