When I went from 4GB to 8 I didn't notice much difference to Poser, except that I could use larger bucket sizes to render and Firefly didn't really cache to the hard drive anymore.  Except for those incessant exr conversions.  What it did do was allow me to have a bunch of programs running straight out of RAM and not the swap file, greatly speeding up applications switching.

For those who have more than 3.5GB of RAM on a 32-bit OS, there are some ramdisk programs out there that can use the extra RAM that Windows can't allocate.  For example, I put 4GB into an old laptop running XP 32-bit, and used the extra 500MB as a temporary drive for swap files, storage, etc.  Not recommending anybody go buy extra RAM because of that, but if you already have it you might as well use it.  Sorry that I can't remember which program I used, it was a while ago and I don't mess with the laptop that much anymore now that I have the desktop built.