My results:

Error rate = 1 every 10, errors = 100098 100545 99931 99905 99434 
Error rate = 1 every 100, errors = 10037 10075 9872 9924 10133 
Error rate = 1 every 1000, errors = 959 978 1012 1032 1041 
Error rate = 1 every 10000, errors = 97 100 109 92 86 
Error rate = 1 every 100000, errors = 11 11 9 12 7

What are you running this on (Machine/OS/Perl Version)? Also, rule of thumb is 30 trials for reliable statistical results. 100 is a safer bet.

Update:(PIII/2.4.18/5.6.1 w/ dev/random) Thanks Zaxo, although to clarify, I was most interested in what the original poster was running on.