ISSUE: My Mac is showing less free hard drive space than I am currently using?
If you turn on the show sizes option in MacOSX
Finder > View > show view options > calculate all sizes
the total folder sizes dont match that of the reported drive free space
further research showed that (among other things)
private/var/vm/sleepimage taking up too much space. (equal to the system ram in the laptop)
Check if you have Trend Smart Surfing installed that the log files are not growing too large
otherwise you can disable safe sleep mode (ie hibernate)
Run the following in a terminal session, reboot and then delete the file
$ sudo pmset -a hibernatemode 0
$ sudo nvram "use-nvramrc?"=false
sudo rm /private/var/vm/sleepimage
This does however mean that if the power cuts to the device while its sleeping - all work is lost.
Handy for laptops to keep this option on.
to reenable change to 3 and =true