A Certain Slant of Light - Laura Whitcomb
I'm not really sure how I ended up reading this book, though I have a feeling it was recommended to me by Amazon at some point.

Anyway, it's a ghost story, though told very much from the perspective of the ghost herself rather than those she affects - Helen has been a ghost so long she doesn't remember much other than attaching herself to various humans over the past centuries. One of them was a poet (which seems to be heavily implied was Emily Dickinson) and it's only when Helen is hanging out with her most recent, a teacher, that she discovers someone in his class can see her.

I don't really want to spoil the concept of A Certain Slant of Light, because it's quite a clever idea, although there was something a little amoral about the obvious lengths to which the concept is pushed within the book. In some ways, it felt as though the author was equally uncomfortable with the situation she created for her characters, as she seems determined at the end to tie up every loose end going, whether that's credible or not.