I have error in nginx error.log:
2010/12/05 17:11:49 [info] 7736#0: *1108 client closed prematurely connection while sending to client,
client: 188.72.80.201, s
I had the same problem and researched on it. In my case this only happens with Webkit (Chrome) browsers. They open connections optimistically more connections than they require if you only load a single resource. In such a case, the excess connection is closed ungracefully or at least without sending any HTTP verb over it. This leads to the mentioned error in nginx.
Regarding #1 answer: Non of the proposed solutions help which is logical as this has nothing to do with proxying.
Regarding #2 answer: proxy_ignore_client_abort on; Does not help in my test.
Unfortunately, I've found no other solution than using
error_log off;