I've seen it offered as a nn for Sheila and Celia in a baby book.
I was just saying to my mum how much I love this name - I was on the phone to her, but I know she gave me a 
face. It's got such a pretty sound, I love the literary connection and I know a very, very lovely woman named Shelley which all goes in its favour.
I think the 'problem' with it, if it is a problem at all, is that it seems a very dated name - a very popular name in the early 70s and I don't know if it's due a revival yet. Having said that, there's a 3 year old Kelly at DD's nursery and, that's unusual among the throngs of Millies and Olivias.
I still love it though.