This fixes most of the UV distortion issues with subsurf. Near seams
however there might still be some distortion, but this should at least
not be worse than before. Subsurf UV is enabled by default on new meshes,
and can be enabled in the modifier panel for existing ones.
Before and after:
http://users.pandora.be/blendix/notsmooth.pnghttp://users.pandora.be/blendix/smooth.png