Flipped Normals covers what you need to know about UV smoothing in Maya, others.

Getting your shells and packing correct is a large part of the UV process. Another factor is trying to control what happens when you smooth the model, either before or at render time. UV seams are something that might drive you crazy to chase down, but not if you understand what’s happening to cause the issues.

This latest tutorial from the team at Flipped Normals shows the problem with UV seams and smoothing and how to fix them. “In nearly all cases texture seams are causes by not understanding UV smoothing.” Henning says, and that is likely true.