I have 8 gigs in my ssetup. I did a little test to see how much i could use up at once. I had gta 4, crysis 2, burning a movie, had YouTube playing on Google chrome, had YouTube playing on Firefox running all in the background while surfing the internet on ie9 and i still had a little over 5 gigs of ram not being used.
PS. 1 HD for porn.... lolol
AMD FX 8350 | 8gigs DDR3 1333 G.skill sniper
IN WIN GRone Full Tower| GIGABYTE 970A-D3P MoBo
EVGA GTX 760 SC| CORSAIR TX Series 650w PSU|
COOLER MASTER Hyper 212 EVO|
Samsung Spinpoint F3 1TB 7200rpm HDD|
128GB Vertex4 SSD