I have only a year and a bit of context since starting at Facebook, but here's my viewpoint.
Facebook isn't trying to move away from PHP as quickly as possible. For years, there have been PHP components (primarily web front-end rendering, aggregation/ranking of data from various sources) and C++ components (primarily high-performance back-end services) and other languages like Python (primarily non-production-path/operations back-end services) and Java (primarily Hadoop-related technologies like Hive and HBase, and services that are heavy users of such), and nothing groundbreaking has changed in this.
New hires use PHP or C++ or whatever language (and often multiple languages) necessary to work on the team and projects they choose to work on. New projects use the languages that make the most sense.
Almost all web front-end work involves PHP - the frameworks and libraries and runtime environment are well-developed, well-tested, well-documented, and well-known.
In terms of HipHop for PHP, the question to ask is: What language could have allowed quick low-barrier-to-entry web-app-centric development in the early days while still delivering the sort of runtime efficiency demanded by the environment? Languages like Python and Ruby may arguably allow the first (but remember we're talking about early 2004 here, so Ruby on Rails was not out, and neither were Django, Flask, and so forth and WSGI had just come out), but would have required a "HipHop for PHP"-style solution as well. Languages like C, C++, and Java may have the runtime efficiency, but it would be a hard argument to say they're as developer-time-efficient as PHP (especially back then).
That's a slightly different question to what one should do today if starting a new venture. And _that_ is also a different question to what Facebook should do today - HipHop for PHP exists, and is delivering performance/runtime efficiency that most languages people mention as an alternative do not. And, the PHP frameworks and libraries and runtime environment exist and allow rapid development of production code. It's actually reasonably pleasant to develop for with those in place.
The HipHop for PHP team is small, but have huge leverage - this small team of reasonably hardcore low-level C++ programmers are making a whole bunch (hundreds?) of PHP developers way more productive (since they don't have to use a relatively slower-to-develop-in language/runtime like C++), and also makes the cost of operating the site go down by making that code more efficient and reducing the number of servers needed.
Facebook isn't trying to move away from PHP as quickly as possible. For years, there have been PHP components (primarily web front-end rendering, aggregation/ranking of data from various sources) and C++ components (primarily high-performance back-end services) and other languages like Python (primarily non-production-path/operations back-end services) and Java (primarily Hadoop-related technologies like Hive and HBase, and services that are heavy users of such), and nothing groundbreaking has changed in this.
New hires use PHP or C++ or whatever language (and often multiple languages) necessary to work on the team and projects they choose to work on. New projects use the languages that make the most sense.
Almost all web front-end work involves PHP - the frameworks and libraries and runtime environment are well-developed, well-tested, well-documented, and well-known.
In terms of HipHop for PHP, the question to ask is: What language could have allowed quick low-barrier-to-entry web-app-centric development in the early days while still delivering the sort of runtime efficiency demanded by the environment? Languages like Python and Ruby may arguably allow the first (but remember we're talking about early 2004 here, so Ruby on Rails was not out, and neither were Django, Flask, and so forth and WSGI had just come out), but would have required a "HipHop for PHP"-style solution as well. Languages like C, C++, and Java may have the runtime efficiency, but it would be a hard argument to say they're as developer-time-efficient as PHP (especially back then).
That's a slightly different question to what one should do today if starting a new venture. And _that_ is also a different question to what Facebook should do today - HipHop for PHP exists, and is delivering performance/runtime efficiency that most languages people mention as an alternative do not. And, the PHP frameworks and libraries and runtime environment exist and allow rapid development of production code. It's actually reasonably pleasant to develop for with those in place.
The HipHop for PHP team is small, but have huge leverage - this small team of reasonably hardcore low-level C++ programmers are making a whole bunch (hundreds?) of PHP developers way more productive (since they don't have to use a relatively slower-to-develop-in language/runtime like C++), and also makes the cost of operating the site go down by making that code more efficient and reducing the number of servers needed.