The wp_list_bookmarks() function is rather expensive. It provides the Blogroll sidebar block. If we don't care about that and remove the call from wp-content/themes/default/sidebar.php we are now at: 

~> siege -b -t30s -c5 http://wp1.localhost
** SIEGE 2.68
** Preparing 5 concurrent users for battle.
The server is now under siege...
Lifting the server siege...      done.
Transactions:		        1000 hits
Availability:		      100.00 %
Elapsed time:		       29.76 secs
Data transferred:	        1.97 MB
Response time:		        0.15 secs
Transaction rate:	       33.60 trans/sec
Throughput:		        0.07 MB/sec
Concurrency:		        4.98
Successful transactions:        1000
Failed transactions:	           0
Longest transaction:	        0.58
Shortest transaction:	        0.07