Meaning
Very happy or delighted.

Origin
This phrase has been part of the language for more than a century. It has become more widely used in the past twenty or thirty years, since it was adopted by English football (no, not soccer please - the game is called football) managers when interviewed after 'the boys' managed a victory.

The increased use of televised post-match interviews and hours of studio commentary during the 1970s brought many football managers before the cameras. These days such men are likely to be cultured and erudite Frenchmen or Spaniards. Before that they were usually British ex-footballers who had left schools in the English or Scottish back streets early to play football. It's fair to say that many of them have little interest in the finer points of English grammar.

From: http://www.phrases.org.uk