Pros
You get to work on the most trafficked websites in the internet. The company uses and contributes to a lot of open source projects, which allows you to learn and be experts on these. You get to work with some interesting and fun people. The company is not just about building portal websites, there are a lot of interesting and challenging projects, mostly involves scaling of some sort. Some groups are practical and allows for innovation from within. The company encourages internal hacks, sponsoring hack day events internally and externally.
Cons
Poor management decision making. Always want to play catch-up, rather than innovate. Old timers tend to be undervalued and under-compensated. Upper management tend to bring in external hires rather than promote from within. Performance follows the 80-20 rule, i.e. most projects are heavily dependent on 20% of the staff. Yet, management tend to split bonuses across the entire team rather than reward the 20 more.