I like this name a lot, although it's very short and in my opinion should be followed by a longer middle name or be used as a middle name. Anyway, as far as I know it's used mainly as a middle name in Wales. It's a great name not only for a girl born in summer. I generally love the idea of using Welsh season names as girl names. I especially adore Gwanwyn.
Pronounced "Hahv". Well, that's how I say it. Welsh pronunciation is "Haav", I think, but I'm English (moved to Wales when I was three). My old primary school headteacher had a baby called Carmel Haf, which I thought was sweet. There are two teachers at my school with the middle name Haf, too. It's an extremely popular middle name in Wales, but I think I prefer it as a first!