As usual, it depends on what you're using it for, and "games" is not very specific. The only time in the last seven years I've hit up against a RAM capacity issue on my own PC was after StarCraft 2 went 64-bit and I had 4GB RAM in my system temporarily to troubleshoot a hardware stability issue.
I have 12GB DDR3 at the moment, from 4GB. I think I took the opportunity to pick up 2x4GB on the cheap, and partly to investigate whether if I had more RAM then more might get used in general. It didn't (excluding caching, for which there isn't an easy way to definitively determine whether there's a performance improvement). IIRC the days when Win7 Windows Update used a lot of RAM might have contributed to the purchase decision as well.
I'd be surprised if there weren't any games that utilised 8GB effectively even on a streamlined system. Some people like to leave all their apps plus 64 browser tabs running during a game whereas I don't (because IMO it's silly to invite potential game performance issues then have to change one's habits greatly to work around it). Some people run an awful lot of stuff in the background like extra utilities or "Internet Security" packages, I don't. There's a lot of room for widely varying answers, so unless people qualify their responses with all of that information (and possibly more), or only quote game RAM usage, then the potential for particularly useful answers to your question is pretty low.