I run RHEL 6.6.
When look at my home folder and run du -sh . it shows 7.2G whereas when I open it via the gui it shows only 6.3GB. I did reboot the machine just to be sure that no more file handles are open.
Where does this discrepancy come from?
du counts sizes based on the blocks used in a filesystem, since that is where the space is important. The properties dialog is probably counting the total of file sizes (based on bytes), so that you can estimate how much space is needed on "any" filesystem.
Because blocks hold many bytes, and partially filled blocks count as much as full blocks (for du), its totals are usually larger than what you get based on just a byte-count.
