[apache]

Well, lets remember we are also using planet destroying weapons, things that 'collapse' black holes, and quantum reactors that can create infinite energy.
A solar sail definitely needs a star nearby to work. I also know that using Newtonian principles, you can definitely get the sail to work in at least a 180 degree arc of movement. Using a magnetic sail would result in the ability to move in a full 360 degrees (ie: both away and towards the star).
Now, as has already been mentioned, there is no such thing as drag in a vacuum. This is true, but much of space is not a total vacuum. A nebula, obviously, is a large area comprised of stellar gasses, and most certainly would create drag. A solar wind also creates a 'drag' force on an object in space, though it requires a very large ship and/or long distances to affect it noticeably. It also depends on direction of motion as to whether it is actually a drag force or a propelling force (the original principle of a solar sail).
So my point is that the solar sail is actually less ridiculous than a quantum reactor or 'collapsing' a black hole, so it should stay in the game. However, it should definitely not be allowed to work in nebula and black hole sectors.