My attempts to upgrade a CentOS-5.1 box running 4.5.10 to 5.0 failed. Everything web-related seems to work fine (it's nice BTW), but the postfix step went wrong somehow. It accepts no mail whatsoever. Here's a telnet test:
% telnet 192.168.1.64 25
Connected to 192.168.1.64.
Escape character is '^]'.
220 zcs.internetguy.net ESMTP Postfix
When I run strace -p on the pid associated with this process I see it waiting on a poll() event. I turned off iptables during the test to ensure firewall rules aren't affecting postfix or ldap in any way.