Pros
Resume value. Having some time at DCI still has value. Sad thing is that the alumni are what made the company great. Once you leave Discovery, you will definitely be more savvy in corporate politics and backstabbing, others taking credit for your work, and dealing with an unstable environment where you don't know if your group will be around next month. They do have stock grants, but with the cuts last year, those long time staff were cut just prior to their shares vesting. So you have to take your chances there. They offer metro and bike subsidies and have some decent benefits, but they continue to get cut as well.
Cons
Transitioning to a 'lean and efficient' culture, i.e. no job security. Executive management has brought in other management from a multitude of other companies and they have diluted the company culture to where it is unrecognizable. Their programming reflects becoming a corporate environment and lacks any originality. The great original docs you see are usually coproductions with other vendors such as the BBC or they commission outside creatives to produce. It says something when "Puppy Bowl" on Animal Planet is one of their highest rated shows of the year. There are now so many new executives that the management structure is hopelessly confused. They are in the process of contracting and have let go hundreds of long time staff. This was primarily a cost cutting move prior to go public and reflects the lack of value for the professional who have passionately built the company. Discovery Communications has sadly turned into a real life Dilbert strip, complete with pointy haired, clueless management.