There's nothing I hate more than MIDI files. I can be sitting all happy and content, just surfing the web, when all of a sudden some crappy version of a halfway decent song blares out over the computer speakers. That's enough to make me want to track down the person who had the smart ass idea of putting up something with the sole purpose of annoying people. And if that's at school, it's 100 times worse. And if the MIDI file is hidden so it can't be shut off... well often I will never return to that page again, rather than deal with a MIDI file. The only thing one can do is turn the sound off your computer and deal with the fact that now your webbrowser takes 30 minutes to load the most simple of pages, heavens help you if you want to look at an image. MIDI files are evil and should be banned from all good websites.
What drives me crazy is that people think having MIDI files around is a sign of a good webmaster. It's not! Putting up a MIDI files takes only a tiny bit of code, it's easy! But they're annoying as hell. It is mortifying to be illegally surfing in the middle of class and all the sudden have a really annoying song blast out at top volume. Everyone stares, you're busted, and you've developed a deep hatred for the owner of the website.