Boo-yah! Some of the Harry Potter main actors try to speak American English.

http://videoeta.com/news.html?id=312...ews-video-link

Cannot say I heard this phrase boo-yah very often though before using TOTV and encountering graciegirl's social circle on the net.

It does seem to be in US pop culture.

[ame]http://www.youtube.com/watch?v=BO36so2Aqps[/ame]