Flow based programming is actually heavily used in music technology, where it actually is a good paradigm for the domain. Max/MSP and its open source cousin Pure Data are interesting, and have dedicated if small communities of not-exactly-programmers using them for real, creative expression.

But most of the proposed use cases are clearly bullshit, and using these languages/programs makes it clear why: organizing code in a single dimension is already hard... organizing it properly and sensibly in two dimensions much more so, as well as a number of other issues with order and tracking race conditions. For anyone who wants to really evaluate this technology, I would give these products a try.

Really though, functional programming and OOP both have sufficient support for data flows that it isn't really an issue for programmers.