Facebook's testing practices and culture of developer accountability help to prevent serious bugs from being rolled out in production code. When a developer's code disrupts the website and necessitates a post-deployment fix, the incident is tracked and factored into Facebook's assessment of the developer's job performance.
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Employees with low karma can regain their lost points over time by performing well—though some also try to help their odds by bringing Rossi goodies. Booze and cupcakes are Rossi's preferred currency of redemption; the release engineering team has an impressive supply of booze on hand, some of which was supplied by developers looking to restore their tarnished karma.
This sounds like Facebook strongly rewards developers who work on trivial, low-risk features rather than larger, more important features. Also, it sounds like bribery factors into your overall job performance rating.