Pros
Fast-paced, interesting work. It's cool to be able to point to a phone and say "I helped make that." Really fun technical problems, engaging challenges, and lots of intelligent people to work with. Good opportunities for learning and growth, though dependent on where you are in the company. The pay is great, though the benefits have been declining slowly, but overall compensation is pretty good.
Cons
When I started at Qualcomm, they were on the Forbes Top 100 Companies to work for list. They haven't been back since, and it's clear why: they stopped treating their employees as a valuable asset, and instead seem to be treating them as expendable assets. I've watched almost half my team go to other companies, but no one in management seems to be panicking like they should be. Qualcomm seems to have no common processes, nor the flexibility to let small groups decide their own processes. "Agile" and "Scrum" are words that are used without any of the actual benefits of those processes. The inefficiency in my group alone is staggering, and proposing improvements gets opposition from the 10+ year veterans who think they're still working at a scrappy startup company. Which leads to the other thing: Qualcomm is an enormous company with tons of revenue, but there are still, for some reason, pockets of the company (or maybe it's universal, for all I know) that act like it's a startup where everyone needs to put in ridiculous hours all the time. If Qualcomm can't meet their deadlines with people working normal hours, then that's a management issue, not employees not working hard enough. There are times when long hours over a short, pre-determined period can result in huge efficiency gains, and that can be worth it. But when it's considered a negative on your performance review that you're unavailable on weekends, while the rest of your work is stellar... well, it makes sense that people (those who could) would try to find a more sane work environment.