Pros
Depending on what store you choose, you'll be around fun people. Free food to an extent (some limitations). Incredibly flexible. Never thought I'd be able to get weekends off, especially in the summer. Definitely an awesome first job. You'll get experience with cash handling, dealing with customer complaints (a lot of experience), problem solving, food prep, multitasking, etc. It really isn't the terrible "McJob" everyone thinks it is. If you're in a good store, you can make it fun, take some of the stress out of it. It all depends on attitude.
Cons
Of course you'll deal with rude customers. Inevitable, really, given that you're really seen as the lowest of the low as far as entry level jobs are concerned. Management is always reluctant to take responsibility for anything. It's always someone else's fault. Sometimes you'll get the managers that hide in the office and text all day. Some employees in my store, at least, speak little or no english, which makes it difficult to communicate quickly.