As I understand it, you don't have to call srand because Perl seeds it to time for you, but if you are writing a script where you want to use rand for some attempt^* at security then you should re-seed it yourself with something more obscure. I usually use some combination of time and place, er, pid. Although obviously you don't want to just xor the two.

^*I say attempt because in the end nothing is trully secure and I don't want to start a debate on it.