1. Necessity. The very first thing that I modded was my first drumset. The retaining screw on the T-bar holding the toms above the bass drum gotten stripped out, so I busted out the drill, followed by a tap and die set. I haven't looked back since.
2. Doom 3: PMC. When I saw that build, I knew I was not alone.
3. My first case mod was inspired by Eddie Van Halen (Frankenstripe mach 1, an very old PII). I've continued on with that theme with Project Frankenstripe, which will be done this spring/summer.