Pros
As Qualcomm is a strong technical leader in the industry, you surely can learn a lot by working here. In general Qualcomm employees are very technical and confident. They are also easily accessible and are willing to discuss technical problems with their colleagues. Location-wise San Diego is definitely a great place to live. It was an enjoyable experience as an intern at Qualcomm.
Cons
The major products of Qualcomm are cellphone chips. They seem to put more emphasis on hardware and systems than software. As a software developer you are probably not going to receive as much attention as system designer. Also the company is pretty large with so many talented employees. It's maybe pretty difficult to climb up the ladder in such an organization.