not much of an issue for me. my G35C came with a clearbra just forward of the rear wheels which gets hit a lot by debris, but not on the Z.
if you're anal it might be a good idea to clearbra along the side of the car at the bottom where there is some kickup. personally in pretty picky about chips and all, but no clearbra installed on my Z.
check out this site for available bra's:
Auto Paint Guard Inc. Tampa Florida Clear Bra 3M Paint Protection Film Car Bras
ryan over there is pretty cool.