Flying in various RvB gangs, as well as a recent Public Agony destroyer gang, I have noticed that a LOT of people just don't seem to understand that focusing fire on the primary is not just a piece of gentle advice from the FC, but rather the difference between victory and defeat. When the FC is calling a primary, unless there is a very good reason, that is what you should be shooting at.
Don't get me wrong, I appreciate that the enemy is splitting their fire. When flying a ship in a 15v15 engagement in RvB I appreciate it when I start taking damage from a single ship, allowing me lots of time to warp out and then return to the battle. I appreciate it that my own fleet is not loosing a ship every few seconds to focused fire. Rather we are all being evenly pelted to one degree or another. Oddly enough when I am called primary I appreciate it that I am getting all of the enemy e-war placed on me. It is good that, three or four tracking disruptors, a few stasis webs and enough points are placed on me that even if I fit nothing but WCS in the lows I would still not be able to leave. I know that my going down at that point is diverting valuable ewar away from my own side allowing them to inflict maximum damage and maneuver as needed.
Unfortunately I know that the same lack of focused fire is happening from my side as well.
In short, when in fleet place your DPS on the primary. Spread your e-war appropriately across the enemy fleet. One side does that and the other does not, they will win.
Example of this would be on the Agony run destroyer fleet I was on. Although there was a large discussion in the forum from some non-agony wondering about the importance of shooting the primary, during the fleet we were able to give the FC the concentrated fire of all of our DPS. And thanks to the enemy fleet on two occasions spreading fire around to me enough that my paper thin thrasher had lots of time to get out of dodge when needed.