This is the definition of HAL according to Wikipedia:
HAL is a Hardware Abstraction Layer and Open-source software Project that allows desktop applications on an operating system to readily access hardware information so that they can locate and use such hardware regardless of bus or device type. In this way a desktop GUI can present all resources to its user in a seamless and uniform manner.
For example HAL can gather information about removeable storage devices and trigger their representation within the user's desktop environment.
KDE has been using this feature to enable automounting, a feature which has been dreamed by most of GNU/Linux users around the world. Windows does this, but some of big Linux distros have started to adopt this also in their release, but not with Slackware. Slackware was designed to be a robust, simple, and working operating system with security on top of new fancy features, so it's not the top priority task for Pat to implement this.
As usuall, you can always install HAL by yourself and recompile all KDE packages to enable automounting if you like, but in my case, i'm fine with what -current offer me. I'm using a simple alias which refers to some command which i put on my .bashrc file to mount and unmount my USB flash disk and it works.