Since this question is posted under the "Meditation" section of the site, then I should only answer simply, and with no elaboration the following:

Not Enough.

Since there is a spiritual tone to the Perl Monks site, though, I should supress the awful member of the Seven Deadly Sins, that being "Greed" (or would it be "Gluttony?") and answer similarly to jepri's answer above and say:

enough.

But "Vanity" being what it is, I cannot resist the temptation to list all of my Perl books.  So, here's my list:

Learning Perl (O'Reilly)
Perl in a Nutshell (O'Reilly)
Perl Cookbook (O'Reilly)
Programming Perl (O'Reilly)
Programming the Perl DBI (O'Reilly)
Perl (Black Book)
mySQL and Perl for the Web (New Riders)
Elements of Programming with Perl (Manning)

God Bless Tim O'Reilly!