Pros
I worked as a summer intern for Dow Chemical and it was a very good experience. My major is chemical engineering and they placed me with an improvement engineering group in Midland Michigan. The supervisors definately take the time to develop you professionally and provide projects with meaningful assignments, reasonable obstacles, and achieveable goals. The people here are very friendly (from the management down to the operators) and you will definately be able to contribute.
Cons
It's in Michigan or Texas (rarely California for interns) Much of the plant is old, with little opportunity to make big technological improvements. Good for people looking to settle down or start a long career in one firm, but not great for young people looking to take large amounts of responsiblities.