-No longer a place for the inexperienced-but-motivated worker to learn on the job. The company is taking far fewer risks on new hires, preferring to bring people in from larger companies (e.g. Google) or more established backgrounds (e.g. business school, consulting firms). In aggregate, this means less creativity, more politics, and more fear of failure.
-Large contractor population. If you're coming in entry-level, you will most likely come in as a contractor rather than a full-time employee. Contractor hiring at Facebook is typically used as a way to get around headcount limits, not as a thoughtful or strategic approach to staffing, and you will probably feel that. There are limited opportunities for conversion (though it's still a great way to get your foot in the technology door).
-Poor investment in and accountability for managers. Many managers at Facebook were thrust into a management role because they were of an appropriate level - not because they are good managers. There is very little accountability for bad managers, and good management skills are rarely counted as notable. Early on, the company set a culture around managers not being different than anyone else - they just happened to manage. It's treated as a side project more than a full role, so there's no particular incentive to develop your people, nor are there any consequences if you're bad for your people.