When was Red Hat / CentOS server installed ?

Just recently I was looking for information when (what date) was particular server installed. We can check it using two ways (both using rpm):

First way: rpm -qi basesystem

Name        : basesystem                   Relocations: (not relocatable)
Version     : 8.0                               Vendor: Red Hat, Inc.
Release     : 5.1.1                         Build Date: Wed 12 Jul 2006 09:08:04 AM CEST
Install Date: Thu 05 Aug 2010 08:42:38 PM CEST      Build Host: ls20-bc2-14.build.redhat.com
Group       : System Environment/Base       Source RPM: basesystem-8.0-5.1.1.src.rpm
Size        : 0                                License: public domain
Signature   : DSA/SHA1, Thu 18 Jan 2007 04:33:57 PM CET, Key ID 5326810137017186
Packager    : Red Hat, Inc. 
Summary     : The skeleton package which defines a simple Red Hat Linux system.
Description :
Basesystem defines the components of a basic Red Hat Linux system (for
example, the package installation order to use during bootstrapping).
Basesystem should be the first package installed on a system, and it
should never be removed.

As you can see in line "Install Date" - this system was installed on Thu 05 Aug 2010.

Second way: rpm -qa --last | tail

gnome-mime-data-2.4.2-3.1                     Thu 05 Aug 2010 08:42:51 PM CEST
gnome-backgrounds-2.15.92-1.fc6               Thu 05 Aug 2010 08:42:51 PM CEST
emacs-leim-21.4-20.el5                        Thu 05 Aug 2010 08:42:51 PM CEST
desktop-backgrounds-basic-2.0-37              Thu 05 Aug 2010 08:42:51 PM CEST
comps-extras-11.1-1.1                         Thu 05 Aug 2010 08:42:51 PM CEST
mailcap-2.1.23-1.fc6                          Thu 05 Aug 2010 08:42:48 PM CEST
termcap-5.5-1.20060701.1                      Thu 05 Aug 2010 08:42:38 PM CEST
cracklib-dicts-2.8.9-3.3                      Thu 05 Aug 2010 08:42:38 PM CEST
basesystem-8.0-5.1.1                          Thu 05 Aug 2010 08:42:38 PM CEST
setup-2.5.58-7.el5                            Thu 05 Aug 2010 08:42:37 PM CEST

The second column indicates exact time/date of installation.