What problems have you had with modifications?

[Sapper]

Its a big world out there in the modification scene, and its a potentially risky business joining in. We all know that nothing is as much of a turn off as a car that doesn't do what its told so I think its time to set out a warning to new commers (like me) as to what will cause you problems.

This is not about bashing certain workshops, this is about talking FROM EXPERIENCE as to what modifications haven't worked on your car, or caused something else not to work on your car.

An example/template (okay, okay, this one's not from experience but its a gimmie), the $20 ebay resistor kits. Why doesn't it work? The ECU can learn around it. How do you fix it? Take it out and reset the ECU.

Lets keep responses concise and aviod post whoring. It'd be great to set this up as a way that someone can check they're not making an old mistake.