Krishan takes some credit for the initial phrase when he remarked that the game AGE of Empires could be take for A Good Effort. This was in conjuction with Keiths continual use of the phrase "good effort" or "poor effort" so thus abbreviations became such as "oh thats A GE" later just abbreviated to GE or PE accordingly. Martin took his own spin on this and later founded the superb HUGEPE family of websites.

Later, a PE came to be symbolised by the ubiquitous MSN Dog emoticon which promised to allow a PE to be declared on MSN much quicker. This reckoned without the fact that it actually took 3 characters to make one (&) and writing PE only took 2. As such, it did not come into wider use until the advent of the Huge PE, which was signified by the mathmatical equation 1 over dog times dog squared:
This proved popular during loading sessions but fell out of use until the advent of the Huge PE group of sites, as well as regular use in football and AGE games.

See also:

VPE - Very poor effort
GE - good effort
EPEPEPEPE - extremely poor effort, the number of EPs dictates the magnitude of the poorness