People are comfortable with things other people like, so if you get agreement from a customer to use them as a case study, put it on your website, and link to it from relevant places.
Richard Stone of Stone Junction PR produces probably my favourite blog from a UK technical PR agency, although that may not be quite the praise it sounds. If you look at the dreadful websites of most technical PR agencies, any information which is newer than about, ooh, 2007 would be noteworthy, never mind something as adventurous as a regularly updated blog. Anyway, I like how Richard manages to shoehorn in what we Twitter users know as "trending topics", and when he mentioned Fifty Shades Of Grey last week (see what I've done here?), I didn't spill a drop of my coffee. But the reference was used to make a good point: when you've done something which might impress future customers, let everyone know about it. People are comfortable with things other people like. If you get agreement from a customer to use them as a case study, don't just do the normal writeup, send it out and leave it at that. Put it on your website, and link to it from relevant places. Make it an aim for every product page on your website to have a link to "see how XXX is using this product here". People are used to Amazon, TripAdvisor and the like: they expect to see reviews and testimonials nowadays, and there's no reason why you can't give them that in a business environment.