Pros
You can wear jeans to work every day & the employee discount (Gap, Banana Republic, Old Navy and Piperlime) seemed popular for those who shop there. For contractors, the pay can be excellent if you ask for it. And you rarely work more than 40 hours weeks, because they don't want to pay the overtime. For employees, the benefits are excellent for the Bay Area - it is the place to work if you are planning to get pregnant. For employees, they won't discourage you from working more than 40 hours if you feel motivated, but it is rarely required. If you are into retail or fashion, this could be interesting to you. If you want a fairly straight-forward, not overly-taxing job, this could also be the right place. And, if you are into UI, they use some relatively new UI technologies since it is a customer site. To sum up, if you are in your 20s - early 30s, already married, own or looking to own a house, have (or planning to have) kids, wear Gap clothing on a regular basis, and live in the suburbs of San Francisco, it is probably the perfect atmosphere for you. Both the longevity and the turnover of employees is high. If you can stand it, people stay for 10, 12, 15 years ... easy job, good pay, and unlikely they will ever fire you if you have been there that long.
Cons
It is not a tech company, it is a retail company that needs software people to run their website. It is fairly straight-forward programming. If you are looking for a challenge or to work with rocket scientist caliber folks, they usually aren't here. While I said the work is not overly taxing, the inefficiencies and obstacles to getting your work done can be quite stressful despite the work not being difficult. Because it is a large company, you are placed in a very small niche position. If you like variety in your work, not the right place for you. Also, because you have such a small job, I found it hard to grow in your career there. Additionally, if you do not fit into the suburban category I described under the best reasons to work there, i.e. you are city person, the culture at the Gap can either make you run screaming or turn you into a cookie cutter drone. Turnover for new hires is very high for all the reasons above.