Hi all,
please excuse my incorrect terms, I'm unsure of some of the technical terms.

So I'm trying to learn UV unwrapping of blender, I've worked out how to mark seams and unwrap, problem is the uv map dose not come out to scale. By this I mean imagine of I make a rectangular box, basically extrude the cube so it's x scale is 5 while x and y are 1. I mark the seams then u to unwrap. However when it unwraps all 6 sides on the uv map are exactly the same size, as if I've unwrapped a cube. Is there a way to keep the scale for the unwrap, eg for a rectangular box 4 will be long while 2 are square.

Thanks in advance.

Well, if you're extruding the cube to make it longer, that means you are adding faces. I just now fired up Blender, scaled the default cube to 4 in the X direction, selected all edges and marked seams, then unwrapped, and it unwrapped as expected, with 4 sides longer than the remaining 2, so I'm not sure what your problem is other than the possibility of you adding faces by extruding rather than simply scaling. If you extrude and add faces, then the long sides will be composed of multiple faces rather than one face apiece as the shorter sides are, so that will affect the way it is unwrapped.

I think there's a bug in the blender build I'm using, (ubuntu 2.11 blender 2.58) if I use the scale x box the object scales but the UV does not. However if I use extrude tool on a face and "pull" the cube to the shape I want it works fine.

If the UVs are not being generated to your liking, you can always just go into the UV editor and tweak them as you need. UV mapping is a fiddly process that usually takes a bit of manual tomfoolery to get it just the way you want anyway.