This is an updated (23/05/2015) video showing how to scrape metadata for Emulation Station with the Raspberry Pi.
I'm using RetroPie 3 beta 2.
You can find the scraper here:
https://github.com/sselph/scraper
You can scrape all systems with this command:
https://github.com/sselph/scraper#all...
Forums:
http://smartretro.co.uk/forums/
http://blog.petrockblock.com/forums/