Those sharkskin lines do cast amazingly well, and I would like to be able to use one but ... I'm one of those unfortunate people who can't stand the sound it makes. I know many who it doesn't bother, but for me it's like fingernails running across a chalkboard.
For anyone out there who can't take the sharkskin sound, look at airflo's ridge lines. That's what I fish. the ridged texture has all the same benefits of the sharkskin, but without the noise (and the extra high price tag). However, the ridge line is made from polyurethane rather than PVC and has a very different feel than any fly line you've ever cast. It took some getting used to but I now love it. Also, I believe their poly lines have a 5 year no crack guarantee.