Wow, thanks for pointing me to the web interface. It looks like couchbase was not actually configured, I had to tell it where to store data, create an admin password, etc. I'm guessing all the cache attempts timed out, which is probably why page load times went so high.
Now it's working, I can view data being cached, but page generation time is still a little higher than with straight mysql. Performance does look slightly better using the memcached plugin which implements getMulti() in PHP as I understand it, so that could be moxi at work.
I also tried uninstalling couchbase and instead installed memcached, very similar performance, still slower than mysql. I think at this point I'll write off this exercise as a useful learning experience, uninstall memcached, and look at alternate performance enhancements.
Thanks a lot for all the input BigBlueHat, couchbase certainly seems more accessible now.
Cheers - Callum.