I commonly talked to people at the NTSSUG that have very large SQL Server environments, (mainly medical and financial), but I personally haven't had a client that requires something of that scale.

Where I encounter colleagues that have insanely huge data requirements are in the physics, weather, astronomy and biology science realm. They truly have "Big Data" issues. Most of their tools are not known in the Microsoft realm, (outside of folks like Buck Woody), but I believe they really could benefit someone with an open mind that loves data. There's some really cool software that's been developed to deal with their issues that I'm incorporating into the "normal" business data world.