(g)Zip archiving of local files?

Hi All, I've seen a couple of references to archiving files using exec() and tar or zip. I am wondering, however, if this is the best/only way to do this. Is this an inherently threaded process, so multiple simultaneous requests won't seriously compromise server performance? What other gotchas should I be aware of? I'm sure that others have researched automatic archiving of files on servers, and I'd really appreciate hearing about your experiences. Thanks, michael geary