Facebook Inc.'s FB +1.91%buoyant stock price has surprised the doubters, including me, by weathering a flood of shares entering the stock market.

The stock's run has been so impressive that it even brought a measure of relief to the social-networking company's underwriters, led by Morgan Stanley MS +1.28%.

Investors might be anticipating a big year-end finish for Facebook. Maybe champagne is going on ice to celebrate the stock's rebound recently. But happy shareholders, analysts and other "friends" of Facebook shouldn't forget all the challenges still facing the stock.

There will be speed bumps ahead for Facebook as 2013 begins. The biggest might be delivering on expectations created by the stock's recent, resilient rally.