Pros
I was an intern at STG for three months. My coworkers were helpful and very easy to get along with, and I very quickly felt like a full member of the team. There is always plenty to do, and you will be expected to keep your nose to the grindstone, but working on such a great team made the responsibilities enjoyable.
Overall, my internship at STG was a great stepping stone into the full-time web developer position that I was hired for shortly after completing my internship.
Cons
None, unless you don't like actually working.