Pros
Free books, access high-profile authors, and the chance to sit in on meetings where big decisions about print runs and strategy are made. Opportunity for mentorship with senior editors and publicists. Great location in the West Village/SoHo. It's a good job to develop basic publicity skills. You have the opportunity to watch a book go from proposal to editorial to design to launch, and that's pretty cool. Benefits were pretty good--fairly comprehensive health/dental/vision packages at a relatively low price.
Cons
It's a lot of grunt-work. A lot of long hours. A lot of tedious tasks, such as list-building and mailing packages. The pay is abysmal, and the work atmosphere is very hierarchical and can be, at times, demeaning to a young person who wants to learn and has ideas. High-stress, high-pressure, and surprisingly fast-paced environment. You get 20 days of vacation even as an assistant, but I never felt comfortable taking my vacation. Promotions are often more title changes than actual promotion--you may get promoted to Associate Publicist, but you'll still be a Senior Publicist's assistant while working on your own full list of books, and the pay raise will be incremental.