flickr - how to scale a php app

with all the enterprise talk floating about, i want to share
this 
persentation from the flickr guys which circulated for a
while but i bet 
some folks haven't seen it. there is some good info on
their scaling 
problems and solutions. no deep details, but still useful.
their usage 
stats are impressive, and i'm sure they have grown
tremendously since 
this presentation.

see http://www.niallkennedy.com/blog/uploads/flickr_php.pdf