Nuke's vanilla sharpen node leaves a lot to be desired -- using it always results in nasty super-black edges and fringing highlights around already-contrasty parts of your image.
Sharpening in a logarithmic colourspace is a solution for this, and LabSharpen can give you nice results too, however both of these options tend to break when you need to be heavy-handed with a soft plate.
Thankfully, Xavier Martín is here to help! He has created a gizmo, X_Sharpen, which "preserves colours, avoids negative lobes and creates minimal ringing and banding on edges". Sounds too good to be true, but it really works! Additionally, he created X_Soften, which uses the same algorithm to soften your image, and you can download both in one package.