Every penetration tester must be up to date on a daily basis about the newest vulnerabilities,pen test techniques,exploits and threats.This will allow him to secure better the infrastructure of his clients by identifying immediately the high risks when conducting vulnerability assessments and penetration tests.A good way for staying up to date is to subscribe to some related info sec mailing lists.Below you can find a list with the most popular mailing lists:

BugTraq

http://www.securityfocus.com/archive/1

Metasploit

http://mail.metasploit.com/pipermail/framework/

Penetration Testing

http://www.securityfocus.com/archive/101

Nessus

https://discussions.nessus.org/index.jspa

Nmap Hackers

http://seclists.org/nmap-hackers/

Web Application Security

http://www.securityfocus.com/archive/107

Honeypots

http://www.securityfocus.com/archive/119

Full Disclosure

http://seclists.org/fulldisclosure/

PaulDotCom

http://mail.pauldotcom.com/pipermail/pauldotcom/

Web Security 

http://lists.webappsec.org/pipermail/websecurity_lists.webappsec.org/