Citrix have published a draft of a report due to appear at ICFP describing their use of OCaml in industry, specifically the Management Tools Team (MTT) responsible for the 130kLOC of OCaml code that runs XenServer. The free and commercial editions of the product are deployed in over 40,000 companies worldwide.
Interestingly, none of the perceived risks associated with using a non-mainstream programming language turned out to be a problem. Good OCaml programmers were in abundance. XenSource was acquired by Citrix without any concern about the use of OCaml. Other teams within the company had no problem contributing to the OCaml code base. The OCaml tool chain turned out to be mature enough to support the project.