Unless you use particularly crappy guy-lines it shouldn't be a problem.  

I use 2nd rate parachute cord for some of mine and they haven't frayed in over 5 years.  I want to replace them with the 3M reflective cord, but can't bring myself to throw out what ain't broke yet.

For tying to rocks I like the 2 rock method.  Tie to one rock, use the other to hold the first rock in place.  Don't over tighten, in fact this is where having a loop of bungie on your tie-points can help.  If "O" is the rock and "\" & "/" is the rope, tie to the rock on the left, 2nd rock goes over the rope:  O\O/tent.  I think this is illustrated in a Bill Mason book.