Right. The only difference between friday and other days is the
obligatory friday prayers. Calling it a muslim sabbath isnt really
an accurate explanation since it is not a rest day but good enough
for a quick understanding.
The Quran says the sabbath is for jews only.
After all .. Islam copied and reinvented the Judeo-Christian
faith.
*Coughs* 
Sorry la for some of the friday disruption. The muslims guys arent
slacking in the mosques or sth. We only hear the 10 mins sermon
(uninspiring btw), pray together after, then CIAO.