Having a name which shortens to a nn does become interesting as you become older - both my parents are always known by the short versions of their names and no-one would ever call them by their full names.
It's almost as if the full name was what they were called by only in very formal occasions when they were young (e.g. if they were being told off), and as soon as they could choose, they opted for a short name. My mum in particular I know put her foot down when she was about 18 or 20 and said 'everyone from now on will call me X'.
Now that we are thinking about names for DD, I asked her what she thought of her proper name, and she said she still likes the fact she has to sign the full name when writing a cheque, for instance, so it's not as if she hates her full name.
I have a name which shortens to a nn too, but in my case the nn is only usually used by friends and even then, not consistently - some friends use the nn, some don't. The one thing I hate - and I don't really know why - is people I don't know well using the nn.
It used to happen at work, and always came across to me as people being over-familiar and chummy, 'presuming' they could use my nn; however at the same time if I said 'actually I prefer to be called X', I would feel like I was being terribly precious and fussy about it. I did eventually ask someone who used the nn all the time if he could call me by my full name, but I did feel bad having to do it. I have no idea why it bothered me so much!