I think obscure is worse than popular. Niamh is incredibly popular with girls her age. But the mythology behind it means a lot to me.
I'd NEVER of called her something like Talliana, Belicity, Ledaisy etc (all names that have been at either her playgroup or nursery, all girls).
But we all have our own limits of obscurity. For example, my list of girls names this time are so far Josephine, Collette, Brigid and Henrietta. When I've mentioned them to friends they've laughed thinking I was joking. Tell me you want to call your baby Jazzmyn and I'd have to walk away very quickly so not to laugh in your face.