I don't think any clipping masks are involved as none of the letters go outside of the boundaries of the image. I think it is pen tool, shape tool, maybe some word art, and I agree that the warp tool may be used to fine tune some edges and fit, but since there is no overlapping of letters on the face, if the warp was used at all, it must have been sparingly. On the body it is a bit more free form, like tattoo art. Interesting.
The artist may have used a couple layers of the man image. One for the translucent layer, one for the stronger contours and shadows, midtone, highlights. The letters may also have used the displace filter to give them contour and I would try a hardlight blend mode for the text, maybe with a screen or overlay layer of the text above that. There may also be liberal use of filter or layer masks to control transparency effects. And I wouldn't exclude layer fx like glows.
And then we find out it's all done with "wordie!" Or an entirely different way. Until you start into "the exhilaration, sweating heat, anticipation and climax of figuring out how someone did something," (thanks Chris) you won't have any idea. If this was done manually, it is pretty sophisticated. For that matter, even if the word art was done with a program, it's still pretty advanced graphics, not Beginner Photoshop.