I was speaking with someone yesterday on this subject, and I hope he won't mind me stealing his point of view, which I agreed with. Porting from something like Winamp and taking it to WB, or going from WB to Litestep, like in jafo's example, is a great way to port. But converting one format into a very similar format, like one desktop enhancer to another, or Msstyles to WB is really pushing it.
And porting removes the incentive to improve your skills. How many porters out there have actually progressed on to making their own original skins? And how many still stick to porting?
I don't see porting as any kind of 'entry level' skinning or a foot in the door. I see making your own graphics and doing something new as being a better way in.
