> In other sub-fields (e.g. OO, logic programming and concurrency), category theory has not so far proven terribly useful.
I wouldn't say that. I don't know about OO and logic programming, but there's a good amount of categorical/homotopical structure lurking around concurrency. See for example [1], [2] or [3].
You mean Goubault-style homotopy stuff. I don't this this is very categorical, e.g. [2] produces a single category, so I wouldn't call this an example of categorical structure.
The Gunawardena paper [1] doesn't exhibit categorical structure either.
I wouldn't say that. I don't know about OO and logic programming, but there's a good amount of categorical/homotopical structure lurking around concurrency. See for example [1], [2] or [3].
[1] http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.46.9...
[2] http://www.researchgate.net/publication/2108154_A_model_cate...
[3] https://en.wikipedia.org/wiki/Directed_algebraic_topology