WhyNotUnmount 0.3 is out now. Version 0.3 provides a number of stability improvements (multi-threading issues were fixed), improved unmounting of volumes, automatic list updating on device mounting / unmounting, and finally, several updated user interface details.
WhyNotUnmount works on Mac OS X 10.4 (Tiger) and 10.5 (Leopard) and comes as a Universal Binary.
For more information on what the application does, please see the original post on WhyNotUnmount.
Download WhyNotUnmount (DMG, 315 KB, Freeware)