For some time I have been working quite extensively with Java and Java-related technologies in addition to all that Erlang and functional stuff I do every day, and I must say that I am really impressed with what is going on in the area where both worlds overlap. A few months ago I was experimenting with JScheme running on Terracotta, but as I told Ari from Terracotta Inc., who became interested in the project, much more interesting would be combining their product with Clojure. I knew that some people had already been thinking about it.
Not much time has passed since then, and guess what. Paul Stadig announced on his blog that he managed to run Clojure code on Terracotta. Today the same guy just made me looking for my jaw on the floor: he made the whole Clojure environment (together with REPL) work on Terracotta! Now imagine Clojure concurrent applications, using Software Transactional Memory distributed across computer network through Terracotta: you can build massive software clusters that can work with incredible performance; you can add Hadoop (distributed file system) and Hbase (distributed database) and be able to build a system that can handle hundreds of thousands of parallel operations and store petabytes of data; you can scale your system up and and down just by adding or removing machines from the cluster. And with modern cloud computing services, like AWS, you can build a large computation cluster or a social networking website with a relatively small budget.
Basically, you don't need much money to start another Facebook. Your imagination and programming skills are your only limit. Good luck!