I released another game called 1-button Suicide Javelin a week ago:
http://www.newgrounds.com/portal/view/602321

Even though the game was quite quickly made (and admittedly not the most impressive thing visually), there apparently was a very bad design mistake that could have been quite easily avoided. This caused the game to lag extremely badly with some people. Now that should be fixed, but most people just tried the unfixed version, which is kind of a pity.

Well, luckily this was just a small game, so this was in fact just a valuable lesson. Now I'll remember to check that a game performs decently on different setups and that it doesn't consume too much memory.