1) Ok proxy cache key is set in /etc/nginx/nginx.conf, I was never experiencing a problem with this so your in a better place to measure the effectiveness for this.
Still having problems logging in and getting the cached "non logged in" version. I just looked at my browser and noticed there is no cookie called "SID" in phpbb3 so you need to make sure what you set is specifically relevant to the actual cookies set by the app. Also you will need to do this so that this only affect phpbb3 and not other apps on the domain. Don't know the exact answer but I am sure with some google time and/or posting in the nginx mailing list, you'll be able to figure it out.
PS. you might need to change the proxy_in_redirect setting back to the default. I can't recollect which one is supposed to remove the port - check docs.
2) Custom 404's work on all the test environments I've looked at so far. Looking back at the fallback 404 stuff this seems to make it not necessary. Or did I miss something?
The fallback 404 stuff is not compulsory. It was useful for a specific application I was using where I knew that just before Nginx could not find something does not mean it doesn't exist (a so called "image firewall" in Gallery 2) so when it returned "404" I passed it to Apache.
3) Ive tried changing between redirect, proxy_pass and a few other settings to catch the 8080 effect. All to no effect, do you have a test environment where you can help me debug it? Given your first comment you've relegated yourself to resident nginx fanboi status, so lets get this to a state where everybody can use it without having to think about it. I think thats going to be the real secret to success, if Plesk users have to make modifications on their own its going be a very high barrier to adoption.
Fanboy? Hmmm. Anyway. People will always have to make modifications on their own and I think the best you can do is give a generic config similar to the one I posted a while back and user will have to manually modify as required as it is simply not possible to provide a one size fits all config.
I seem to recollect sage words of wisdom from you to this effect when I asked whether the ART Nginx install package could set up so that it starts on reboot. You said then that it had to be done so that users have to set this up themselves. I would have thought that making it start on reboot is infinitely more straightforward than a global, every possibility config.
On the test environment, I am setting up a linode to try out Cherokee and also a switch to Ubuntu instead of Centos but this is tied up for the moment. Perhaps you could give the mailing list a shot.
4) On cherokee, maybe. Do you know if a) what its license is (We've got to be allowed to redistribute it) and b) does it support mod_security, ioncube, zend, etc.
License:- Creative Commons
mod_sec:- No. (but don't tell Mike
ioncube:- It should since this is a php thing
etc:- Not sure
I haven't tried it yet but after playing with Nginx for a few months, I am looking to something else to become a fan of.