There seems to be a lot of ex SP on Linked-In who list their Post Nominals...but I estimate (very unscientifically) that about half are people list obscure industry-based diplomas, or qualifications from rather random, non-accredited colleges. It's as if ex SPs need to 'big up' their backgrounds, whereas in most cases there's no need to do so.
I use my post-nominals in work (as it is expected) but UK military seem to be about the only group who do it on a regular basis.