Avantages
eBay is a good place to learn about running a high-scale Web site, both operations and software-wise. Work environment became much less stressful in the last two years after Lynn left (no 2AM anymore!). There is always some level of satisfaction from fixing the site used by so many users. If you're lucky, you can get to a team with many great engineers. Moving between the teams and advancing career are reasonably easy. And the company generates tons of profit, which makes employees feel more secure.
Inconvénients
Bureaucracy in software engineering is depressing. There's less and less room for engineering experiment, as many attempts would get overwhelmed (or slowed down to a halt) by politics or requirements to prove profitability of ideas. A lot of great engineers left in 2005-2007, and new hires are not of a that great quality. Politic games and pretending that everything works just great affected morale of many engineers. And as you all know, more and more sellers hate changes being done by eBay. It is now difficult to find positive posts about eBay on any blogs... How sad. eBay used to be a wonderful company for customers and employees, I really enjoyed working there.