Google top 1000 list:
Place  16 Varnish running on www.twitter.com (search.twitter.com) 
Place  49 Varnish running on www.weather.com (www.weather.com)      
Place  53 Varnish running on www.answers.com (www.answers.com)  
Place  80 Varnish running on www.globo.com (www.globo.com)          
Place 116 Varnish running on www.nytimes.com (or so they tell themselves) 
Place 160 Varnish running on www.slideshare.net (www.slideshare.net)       
Place 186 Varnish running on www.livejournal.com (www.livejournal.com)   
Place 208 Varnish running on www.mercadolivre.com.br (www.mercadolivre.com.br)
Place 215 Varnish running on www.y8.com (www.y8.com)                  
Place 313 Varnish running on www.robtex.com (www.robtex.com)                 
Place 368 Varnish running on www.manta.com (www.manta.com)               
Place 370 Varnish running on www.squidoo.com (www.squidoo.com)   
Place 403 Varnish running on www.taleo.net (www.taleo.net)              
Place 488 Varnish running on www.gazeta.pl (www.gazeta.pl)               
Place 564 Varnish running on www.wetter.com (www.wetter.com)            
Place 579 Varnish running on www.spiegel.de (www.spiegel.de)         
Place 596 Varnish running on www.merriam-webster.com (www.merriam-webster.com)
Place 603 Varnish running on www.wat.tv (www.wat.tv)             
Place 614 Varnish running on www.rutube.ru (www.rutube.ru)              
Place 619 Varnish running on www.mercadolibre.com.mx (www.mercadolibre.com.mx)
Place 652 Varnish running on www.zappos.com (www.zappos.com)             
Place 693 Varnish running on www.xpg.com.br (www.xpg.com.br)                
Place 700 Varnish running on www.espncricinfo.com (www.espncricinfo.com)
Place 722 Varnish running on www.stumbleupon.com (www.stumbleupon.com)   
Place 739 Varnish running on www.wwe.com (www.wwe.com)                      
Place 766 Varnish running on www.kapook.com (www.kapook.com)             
Place 795 Varnish running on www.mercadolibre.com.ar (www.mercadolibre.com.ar)
Place 870 Varnish running on www.xywy.com (www.xywy.com)                  
Place 885 Varnish running on www.break.com (www.break.com)            
Place 969 Varnish running on www.mobifiesta.com (www.mobifiesta.com)         
Place 987 Varnish running on www.mercadolibre.com (www.mercadolibre.com)
Place 991 Varnish running on www.popcap.com (www.popcap.com)       

Global Alexa toolbar users:
(Note that facebook (#2) is using varnish, but this is not automatically discovered
Place   9 Varnish running on twitter.com (search.twitter.com)
Place  76 Varnish running on livejournal.com      
Place  95 Varnish running on weather.com      
Place 111 Varnish running on globo.com          
Place 112 Varnish running on stumbleupon.com 
Place 144 Varnish running on answers.com       
Place 203 Varnish running on wikia.com             
Place 220 Varnish running on squidoo.com       
Place 241 Varnish running on espncricinfo.com 
Place 251 Varnish running on slideshare.net 
Place 373 Varnish running on soundcloud.com        
Place 389 Varnish running on drupal.org     
Place 392 Varnish running on mercadolivre.com.br 
Place 403 Varnish running on businessinsider.com 
Place 435 Varnish running on forbes.com          
Place 441 Varnish running on gazeta.pl           
Place 479 Varnish running on posterous.com