[UberGoober]

I'd say it depends on the mesh and on the crash. I have a mesh coat with leather over the forearms, shoulders and back protector. I have seen photos where mesh jackets wore through in small spots during a slide and others where the outer layer wore through but the inner layer didn't.

My thoughts are that mesh is OK for most street riding but that you should probably go with leather for more agressive riding. Be aware also that mesh is usually a use it once and throw it away proposition. Minor cuts and abrasions on the shell will make it pretty susceptible to tearing in later crashes.