I was looking through a religious book from the 1950s and saw Mí na Feabhra and Mí na Márta referred to as Mí na Féile Brighid and Mí na Féile Pádraig. Is this still commonly used? Is it more of a pious thing or is it a folk thing?

i have never seen them

These were the popular names for a long time until the literary names Feabhra and Márta were reintroduced through the school system. Also Eanáir in place of colloquial an chéad mhí den bhliain. The popular terms were still preferred to the learned ones among Gaeltacht speakers in the middle of last century, but I never see them in print these days and imagine that they are used less and less in speech.

Mí na Féil' Bríde, yes, and also Mí na Féil' Eoin for June. I've not heard Mí na Féile Pádraig myself but it may well be in use.

Ainm eile ar mhí na Feabhra ná "Mí na bhFaoilleach" - ach bí ar d'airdeall! Má deireann Albannach "Faoilleach" leat is í an mhí roimhe a bheas i gceist aige.

I have to correct myself. It was spelled Mí na Féile Brighde. That is now Mí na Féile Bride as Abigail pointed out. When I searched the Internet, very few hits came up, so that made me think it wasn't very common, but I had nothing to confirm that among Irish speakers, except the Daltaí boards(!). I thought it may have been patterned on the other non-Roman month names like Mí na Samhna and Mí na Nollag.

(Message edited by seánw on August 04, 2009)

Many months have different names in the dialect, although you won't see them much nowadays because most book and internet stuff is in the CO.
But if you have a look, for example, at Mac Cionnaith's dictionary (a dictionary published in 1947 with many dialectal variants), you'll find some of the other names.

Dinneen also gives a fair number of them.