Now that the "a stoir" issue has been resolved, can someone give an authoritative gloss on "Erin go bragh", which seems to be US usage, though I think I have also seen it in photographs of banners/flags at early Gaelic League events in Ireland? Or did some Irish regiment in the British army use it as a regimental motto?

"Erin" is clearly wrong, as Bill Kennedy points out - it's no more than a misspelling of the genitive or dative cases of "Eire".

But I am also unaware of any Irish expression "go bragh" or "go brach". I have tended to assume that it was an attempted phonetic rendering of "go brea" ("nicely" or "well"), and that it was probably a made-up way of saying "Up Ireland" (which would loosely translate into American as "God bless America", a rare instance of Ireland being more secular than the US ;o} ). Can anyone confirm or offer a better interpretation?

By the way, "I don't want to be pedantic, but" the vocative particle in English is written "O", not "Oh" - and before some fellow-pedant hits back, I left out the accents from the Irish words deliberately for reasons of keyboard compatibility.