It's taken me a week to find it, but I've finally found how to make the SD card reader work properly on my Acer Aspire One A150 with Slackware 13.37 (stable). (Sorry if I'm repeating your work - but I could not find the solution on this site)
Previous to this, the card reader would only register if the SD card was inserted prior to boot.
To /etc/rc.d/rc.modules add the line:
and the card now mounts when inserted as expected.
Simple - when you know how.