Hugh Williams' Blog: "PHP at Scale" panel discussion at the PHP UK Conference 2012
The good news was that Rasmus and Nikolay couldn't see any reasons why PHP was particularly challenging. What we saw were general challenges in scaling applications to large traffic volumes - and that's pretty much where the panel discussion went. Here's a few key points from the discussion.
Highlighted points included: removing bottlenecks to help performance (simple in theory, hard in practice), the fact that PHP should never be the bottleneck, the "odd direction" of HipHop, challenges/growing pains in moving from startup to a large web property. There was also a less technical discussion about "scaling teams" and finding the right (motivated) people to do the job.