I have had lots of thoughts about it and, eventually, decided to only have local individual highscores, so cheating is not really beneficial for player and not harmful to others. Yet my game is just a simple minesweeper, and there were people who complained about the lack of competitive table.
Option 2, is approach taken by WebSudoku - to show your place "among the people of internet". So you will not see any other results, and people wont see your results - but you can compare yourself to crowd.
p.s: And seriously - any kid with Firebug/WebInspector can easily hack your JS game and, eventually, to be able to reach very high score.
