Note that an 8-character alphabetic password has log(26*2)/log(2)*8 = 45.6 bits of randomness. As of 5.20, perl uses drand48, which is named for its 48 bits of internal state. Nominally, it has enough randomness to fill that password, but it's seeded with only 32 bits. So if your program starts up, generates one password, and then exits, only about 1 in 12000 (= 2**(45.6-32)) of the possible passwords can be generated.

If you're generating many passwords at once, they are going to be highly correlated. Someone can in principle use their password to guess what the next password will be. There are about 5 or 6 (= 2**(48-45.6)) possible next passwords. An old node of mine shows how this can be done (Predict Random Numbers).

Bottom line: Use a secure random number generator.