Yeah I've been there with the homebrew one inspired by Hugo's original one about 4 years ago. I had a 3.5" drive mounted horizontally (label up) without any major troubles. I had some minor shock absorption.

First drive was a 6.4Gb Quantum Fireball and I used it for about 1 year with absolutely no trouble. It's still running today in my firewall.

Second drive was a 30Gb Samsung. It developed a few bad sectors after a while and finally died after about 1 year of use in the car and 1 year in a home PC.

Edit: And I never bothered with any code to spin the drives down either. That was my biggest problem - the PSU could only just supply enough +12V current to spin up the drives so I kept them spinning all the time.

YMMV