I am using TOP and I noticed that the FREE memory and the USED memory are inverted!!!
You can compare (in the image) the output from Conky (at right) with the output from Top (at left). They are inverted, with Top showing the wrong.
top: procps version 3.2.8, Xubuntu 10.04.1 LTS, Linux dell-laptop 2.6.32-26-generic #48-Ubuntu SMP Wed Nov 24 09:00:03 UTC 2010 i686 GNU/Linux