I got into another "chat" with someone who was mocking Rails due to the fact that he keeps seeing a cat when he tries to use Twitter.

"This app is slow, therefore Rails can't scale"

This is an old argument of course.

The problem is that Twitter doesn't scale in the same way as many Rails applications.

I talked about how Scaling out 37 Signal-style applications is convenient. In many ways, Twitter is more similar to a real-time stock exchange than a simple CRUD application. Tweets may not be quite as important or timely as $$$ (stock info), but there are some similar issues.

This is why, for Twitter to scale nicely, it probably makes sense to use a message bus that can scale out nicely. Pull versus Push / the loose coupling can really help you out, and you can copy what NASDAQ does instead of Basecamp.

The message bus could be Ruby, could be ActiveMQ, could be TIBCO Rendezvous.

This architecture change would surely do a lot more for you than "re-write it in Java", which may give you a slight boost (e.g. more out of less machines), but is like adding lanes to 101 instead of using public transport.