They use facebook ids everywhere which are integers represented as strings.

I guess with HTTP, every get/post/cookie parameter is a string... they might have found it was less expensive to simply not convert them.

i found it pretty inspiring. not only was it a neat example of coding with instruction-level parallelism in mind, but a concrete demonstration that it did indeed provide significant speedups in a piece of code that people have been using for decades (and which had presumably already been optimised for the single-everything cpu case)

Perhaps they are referring to HTTP? The GET and POST params come in as strings.