With regards to the corporate world: The trend for the last year is to purchase all new PCs with 8GB or RAM. Honestly 4GB is the bare minimum once you factor in Windows, Anti-Virus, running browser, and an open MS Office document. And being that you don't just find machines with 6GB, the next best option is to double for 8GB.
OTOH, if someone wants to upgrade their existing machine, I recommend going to 16GB. My time to scope part, install, and validate + the cost you pay for the part = not worth going to 8GB of you plan on keeping the computer around for its remaining lifespan. Don't get me wrong here, I'll sell and install the 8GB kit for you if that's what you really want. In fact, it might be all that's needed if you have free slots available vs pulling all existing modules and swapping with new.
For Adobe junkies, CAD-o-holics, and Devs, You get 32GB. Anything beyond that and you're looking at Xeon based architecture; which BTW is a whole other ball game as ECC memory isn't cheap in comparison.