i just noticed that nautilus on ubuntu 11.10 shows all files with bigger size !!! but when u copy the file to another operating system , u can see the real size of the file
for example when i download the Ubuntu Server amd64
it was about 682MB and after downloading it became 715MB
so when u see the size in properties in bytes its 715,436,032 bytes , divide it on 1024 twice to get it in MB u get the result 682MB , so nautilus doesn't calculate this !!!!!!!
i guess this is bug :S
im running on Ubuntu 11.10 64 Bit