I can't recall the last time I heard anyone use this interjection, but I know it was used in my family when I was growing up. Of couse, I preferred attagirl! seeing I'm female. I suppose the current household equivalent would be the frequent use of good girl! when my dog Penny earns some praise.
I'd have thought it was a typically Australian usage, but Word A Day is an American institution, so I guess it might be a more universal phrase than I realised.
The online Macquarie thesaurus (Australian) includes attaboy in a selection of interjections synonymous with well done!
good for you, good on you; Informal: (you) (little) beauty, attaboy, attagirl, beaut, bewdy, bully, bully for …, curl the (or a) mo, good egg, good iron, good show, great, man, nice one, onya, that's the shot, your blood's worth bottling;I've never used onya as an interjection, but I have used good onya (meaning good on you).
A Word A Day emails include a quote or two to show the usage of the daily offering, and here are the quotes for attaboy:
"The employees are not asking for a whole lot -- just an Attaboy! or an Attagirl! And news of this small gesture moves like wildfire through the ranks."So...
Labonita Ghosh; Five Ways to Reward the B-player in Your Team; The Economic Times (New Delhi, India); Feb 1, 2011.
"Dr. Burton refutes the notion that present-day parents have coddled and attaboyed their children."
Michael Tortorello; Mom, You're One Tough Art Critic; The New York Times; Jan 27, 2011.
the first quote shows the word is used in India and the second one shows it has morphed into a verb. Verbing is one of my favorite linguistic processes. As Mark Liberman on Language Log says, '... you can pretty much verb any noun you want to verb.' There are myriad examples of nouns used as verbs, from Shakespeare's day to today, but I don't know many examples of interjections as verbs. (I'm sure linguists know lots of them, lol.)