A new feature in Blender 2.5 that's hard to spot is color management. It 'linearizes' colors for internal processes such as rendering and compositing and applies the appropriate gamma corrections for your display device.
Blender 2.5 includes a first version of Color Management. Currently this is limited to ensuring Linear Workflow during the render pipeline - gamma corrected inputs are linearized before rendering, the renderer and compositor work in linear RGB color space, and is gamma corrected back to sRGB color space for display in the image editor.
Future work may include support for display profiles, LUTs, and finer grained control over input/output conversions.