Given the question of whether I could have 48 CPU cores at my disposal, it would really depend on what I'm applying it towards.
If I were building such a system for work, then given a massive pool of RAM, I could virtualize my employer's entire server setup: it would be highly efficient power-wise, and much easier to manage. I imagine our server rack would be a lot cooler as well.
What would I do with it personally though? My government is currently on a push to encourage more high-speed broadband use by its citizens. However, this will take some time to come to fruition: in the meanwhile, there are plenty of places with "high speed" connections that barely manage 1.5mbit download rates, and upload rates much smaller. I am aware of file-management techniques such as: alternative compression formats; re-compressing existing archives; re-compressing image files without quality loss; minimizing scripting files; and optimizing web pages to be less redundant. I could build an online facility to take archive submissions from users, and create download-able versions of their websites, that would be faster and use less bandwidth than before. Gains per optimized site would probably yield a 10-25% improvement. I could implement this with open-source tools, and provide the platform freely, so that others could provide this service as well.