i have 8 gigs and have never seen PP 2010 use more than a couple gigs tops - even with lots of large .psd textures. of course i mainly render figures with props and shaders - some people have created some pretty elaborate crowd/battle scenes in Poser and im not sure if theyll actually make Poser utilize significantly more RAM, or just run much slower.

that said, im thinking about upgrading soon to 16 gigs of RAM, but its certainly not for Poser - its for Zbrush and C4D, and multitasking with Photoshop. ive been getting lots of Zbrush out of memory errors lately, and its a pain in the ass to have to close every other program and compact memory before i perform some operations in zbrush.  every time i need more RAM its for content creation, not rendering. my laptop has only 4 gigs of RAM (albeit its running a highly optimized and stripped down version of windows 7 64), and it runs Poser just fine.