Tweaks That Don't Work

This may be the subject of some discord, but a great community service would be to help others not waste money on snake oil.

Please let us know what you've tried that had no impact - or negative impact, even - on your system. Also, if there are tweaks or products that are only useful on some systems for whatever reason, please let us know what kinds of systems do and don't benefit from the particular products.

Some of you out there have tremendous experience trying to squeeze every last ounce of performance out of your equipment and probably have a laundry list for us - let's hear it!
I didn't try the foil on a CD, because I only use LP records.
Maybe that was the problem.

I did cut the recommended sizes and shape, and put them on each item in my system.

I left them there for a year. After removing, no difference noticable.

Oh well.
TWL: You may need to reapply the foil, being sure to ignore any protests from your components. Most commonly reported? A barely audible murmuring that sounds something like "Curses! Foiled again!!"
I'll be posting more about Richard Hardesty's work on other subjects, but he had just a short bit to say about tweaks. Generally, I believe his position was most tweaks are not worth the money spent (I assume directed at commercial tweaks), which mirrors a comment made in this thread. I believe he also infers that most tweaks damage the sound (or the accuracy of the sound, at least) rather than help it.

If you agree with Hardesty's theories - and particularly his position on tweaks - then most tweaks are useless or worse, harmful.

PS: when I say "he had just a short bit to say about tweaks" I'm referring to a segment in his "Audio Perfectionist Journal," not referring to an actual dialogue I have with him.