Pros
Obviously, the NIH is probably one of the only places in the US where you can do cutting-edge biomedical research with fairly flexible budgets. For postdocs, they also provide opportunities to attend meetings, although this has decreased during my time here due to the budget crunch.
Cons
The salary for a postdoctoral fellow is absolutely horrible. I have been here for 5 years and we have had no pay increases, while the cost of living goes up and up and up. Living in the DC region on the pay they give is pretty much impossible unless you are willing to give up comfort - who works hard enough to get a PhD in order to do that? You had better be married with a second income, and preferably without children if you want to make it work. It is very depressing when there are technicians without anything beyond a Bachelor's Degree making twice what postdocs make, and they get benefits too.