A perfect game of PacMan is defined as a game in which the player scores 3,333,360 points without losing a life. This score is achieved by eating every bonus fruit that appears, eating all four monsters for all four energizers, and, of course, eating all the dots on each level. A player can keep this up for 255 levels, after which the machine crashes (due to a notorious FixedQuantityOverflowBug) and the game must end.
The first such game was played by Billy Mitchell in New Hampshire, in the year 1999, over a period of six hours.
Time well spent, I say.
Story here: http://web.archive.org/web/20040209022631/http://www.twingalaxies.com/PR-Pac-Man_World_Record.html
Quote from the article about a rival: On May 8, 1999, during Funspot's First International Classic Video & Pinball Tournament, Rick Fothergill, of Hamilton, Ontario, Canada, grabbed headlines with CNN, Associated Press, the Boston Phoenix, Boston Globe, and CBS Radio Network News, when he fell a mere 90 points short of a perfect game, scoring 3,333,270 points.
IIRC, after numerous levels (well into the "keys"), the monsters no longer turn blue when the energizers are eaten. I'm assuming the 4*3000 points (200 + 400 + 800 + 1600 = 3000) for monsters on those levels don't count?
It's possible to get points on the last level (the one that crashes) -- about half the level generates first and can be played for points however not all the dots are reachable so the level cannot be beaten.