The name of the vhosts (like for example site1.com) doesn't appear anywhere in the access logs.
/var/log/ispconfig/httpd/site1.com/20120512-access.log
Code:
207.241.226.112 - - [12/May/2012:00:51:22 +0000] "GET /robots.txt HTTP/1.1" 200 24 "-" "ia_archiver(OS-Wayback)"
207.241.224.41 - - [12/May/2012:00:51:23 +0000] "GET /robots.txt HTTP/1.1" 200 24 "-" "ia_archiver(OS-Wayback)"
95.108.150.235 - - [12/May/2012:12:52:49 +0000] "GET / HTTP/1.1" 200 868 "-" "Mozilla/5.0 (compatible; YandexBot/3.0; +http://yandex.com/bots)"