Pros
You get to make a difference on products that people love to use. You might have more influence on the overall product at a smaller company, but you can have a significant impact on products that millions of people use and which set the direction for entire industries. Nothing compares to the thrill of having a product you've worked hard on being announced at Macworld or WWDC to glowing reviews, and then seeing people all over the place using it. Also, unlike some other large companies, Apple's teams run small. This means that nearly everyone's working on something really important to their product, and that at least within your own area of influence it's pretty easy to get things done.
Cons
The company's expectations are very high. Product schedules are aggressive and the quality bar is high, so pushes to get releases out can be tough. Management is often willing to let you work as hard as you're willing to, which in retrospect can be more than you really wished you'd worked. Apple doesn't offer quite as much vacation time as some other companies (though Christmas through New Year's is a free vacation every year), and a bit more time off would help. Also, the company is very fast-paced, so things can change quickly. Get used to decisions being made one day and changing the next, but on the plus side the final decision is nearly always the right one.