This is IMO a more relevant question than it seems. You'd think so, but it's absurdly rare to see real-world uses of demo techniques like this (not only talking about fluid-sims, here). I long wondered why this is (easy answer: because it's hard).

These things are often designed to run very efficiently and getting maximum effect out of limited hardware and memory. It's perfect for, say, a small indie game looking for a cool background effect or something. I'm sure there's examples, but I couldn't even come up with one.