With patch 4.0.6, we are increasing this buff to 5% damage, healing, and health per random player, up to a maximum of 15%.
So, suppose guild group A of 4 players finds random B.
Each player in A gets a 5% buff. Does player B get 15%?
Sounds like a good and well thought through change, anyway. I mean, not that I join PuGs, but I feel for the people who don't have any alternative.