Thanks for the advice Piotr, but instead of helping me, it just complicated the situation a whole lot more :P

2010/01/05 01:22:28 [notice] 4020#0: signal 17 (SIGCHLD) received
[b]2010/01/05 01:22:28 [alert] 4020#0: worker process 4024 exited on signal 11[/b]
2010/01/05 01:22:28 [notice] 4020#0: start worker process 9274
2010/01/05 01:22:28 [notice] 4020#0: signal 29 (SIGIO) received
2010/01/05 01:22:29 [notice] 4020#0: signal 17 (SIGCHLD) received
[b]2010/01/05 01:22:29 [alert] 4020#0: worker process 5209 exited on signal 11[/b]
2010/01/05 01:22:29 [notice] 4020#0: start worker process 9294
2010/01/05 01:22:29 [notice] 4020#0: signal 29 (SIGIO) received
2010/01/05 01:22:31 [notice] 4020#0: signal 17 (SIGCHLD) received
[b]2010/01/05 01:22:31 [alert] 4020#0: worker process 5171 exited on signal 11[/b]
2010/01/05 01:22:31 [notice] 4020#0: start worker process 9321
2010/01/05 01:22:31 [notice] 4020#0: signal 29 (SIGIO) received
2010/01/05 01:22:32 [notice] 4020#0: signal 17 (SIGCHLD) received

Looks like nginx is segfaulting.. any ideas of what could be causing this?

Something to do with:

location @fallback {
internal;
fastcgi_param SCRIPT_FILENAME $document_root/backend.php;
fastcgi_param QUERY_STRING $query_string;
include fastcgi_params;
fastcgi_pass 127.0.0.1:9000;
}

I would assume....