Not the best case study in the world, but a fun one:

I was bored at work seven years ago today. I can tell that because I was just looking through old emails and seven years ago today I was emailing Seb with an 'audit of recent text messages'. Here is who I was text messaging seven years ago:

What fun to have that data and be able to look back - not at who I remember being in touch with - but who I was ACTUALLY in touch with. There are some names on there I had completely forgotten about! One good reason to gather data and keep it laying around, I guess. I'll probably dig it out again in another seven years and then I'll really appreciate it!

(If I hadn't swapped phones so often I'd have kept all text messages since then and I could do some trend analysis. But technology has sadly not made this possible, but I'm starting again now with my iPhone and this helpful site) 

(As shown in a previous post, there is a neat tool to do this kind of analysis on your Gmail, but I'm not enough of a nerd to be able to get it to work. Rubbish.)