Avantages
eBay gives you good experience working on a high-traffic, high-visibility web site. It's a company that's great to have on the resume. You will learn a lot about development and business in a fast-paced eCommerce company. Also, eBay ownes a lot of companies so the opportunity for internal transfer to keep things new and interesting is good.
Inconvénients
eBay is a big company that has not quite outgrown its fast paced startup roots. It is still very hard driving. Depending on where you are in the company, you may be worked pretty hard. Although it is not nearly as bad as it used to be. I set my limits now and don't have bad working hours. eBay is also going through some tough times right now trying to get their growth back, and that affects the employees with constantly switching priorities and high-pressure projects. As far as technology, you'll work on some cool stuff but if you always want to be on the cutting edge working with the latest frameworks this is not the best place to be.