Study your Callgrind graph carefully!

gdb to see what is going on
% gdb /usr/sbin/apache2
GNU gdb 6.6-debian
Copyright (C) 2006 Free Software Foundation, Inc.
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This GDB was configured as "i486-linux-gnu"...
(no debugging symbols found)
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
(gdb) b php_verror
Function "php_verror" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (php_verror) pending.
(gdb) run -X
...
(hit page)
...
Breakpoint 2, php_verror (docref=0x0, params=0xb779dc6b "", type=2048, 
    format=0xb758b640 "It is not safe to rely on the system's timezone settings.
Please use the date.timezone setting, the TZ environment variable or the 
date_default_timezone_set() function. In case you used any of those m"...,
 args=0xbfa3d1cc "??X?\210?\037\b") at /home/rasmus/php52/main/main.c:569
569		char *class_name = get_active_class_name(&space TSRMLS_CC);
(gdb) bt
#0  php_verror (docref=0x0, params=0xb779dc6b "", type=2048, 
    format=0xb758b640 "It is not safe to rely on the system's timezone settings.
Please use the date.timezone setting, the TZ environment variable or the
date_default_timezone_set() function. In case you used any of those m"...,
args=0xbfa3d1cc "??X?\210?\037\b") at /home/rasmus/php52/main/main.c:569
#1  0xb74c19d1 in php_error_docref0 (docref=0x0, type=2048, 
    format=0xb758b640 "It is not safe to rely on the system's timezone settings.
Please use the date.timezone setting, the TZ environment variable or the
date_default_timezone_set() function. In case you used any of those m"...)
at /home/rasmus/php52/main/main.c:733
#2  0xb727d719 in guess_timezone (tzdb=<value optimized out>) 
    at /home/rasmus/php52/ext/date/php_date.c:603
#3  0xb727d795 in get_timezone_info () 
    at /home/rasmus/php52/ext/date/php_date.c:660
#4  0xb727f24e in zif_strtotime (ht=1, return_value=0x8327b7c, return_value_ptr=0x0,
                                 this_ptr=0x0, return_value_used=1)
    at /home/rasmus/php52/ext/date/php_date.c:1113

Set your default timezone in php.ini file
date.timezone = "America/Los_Angeles"

Front page - After restarting server
Transactions:		        5362 hits
Availability:		      100.00 %
Elapsed time:		       29.63 secs
Data transferred:	       63.05 MB
Response time:		        0.03 secs
Transaction rate:	      180.97 trans/sec
Throughput:		        2.13 MB/sec
Concurrency:		        4.99
Successful transactions:        5362
Failed transactions:	           0
Longest transaction:	       25.02
Shortest transaction:	        0.00
Query Page
Response time:		        0.02 secs
Transaction rate:	      283.04 trans/sec