Pros
The Smithsonian Institution is prestigious, and it feels like an honor to work there. It affords people opportunities to do work that they would be able to do nowhere else, in interesting and esoteric fields of study. Consequently, my coworkers are all extremely smart, dedicated, and passionate about their work, and the overall work environment is highly intellectual. From an employment perspective, the workplace is friendly, tolerant, and accepting, and I have a very healthy work-life balance. The health, vacation, and retirement benefits are top-tier for an American organization (if you qualify for them). Overall, I enjoy working for the Smithsonian. I recommend it as a good place to work, because it affords its employees the chance to do very fulfilling work. That said, prospective employees need to be aware of the organizational issues I discuss in the cons section.
Cons
The HR employees are helpful and friendly people when you talk to them one-on-one. That said, as an organization, OHR is broken. It is EXTREMELY slow at processing HR actions, it makes a lot of mistakes, and the hiring/promotion process is completely opaque. At this point, it is expected that hiring actions (new hires, converting contractors to employees, promotions) will take MULTIPLE YEARS to go through. This is not an exaggeration - this is my personal experience, and the experience of many of my coworkers. Because OHR is dysfunctional, there is an overreliance on independent contractors - people who are doing the same great work as staff, but with zero benefits and more income tax burden. Independent contractors do often convert to full time employees, but there is absolutely no guarantee of this. Finally, because funding is limited and there is such high demand to work for the Smithsonian, they can and do lowball employees on salary. Many employees are hired at the equivalent of a GS-5 or GS-7 grade. Look at GS salary tables for the Washington DC area and really consider whether you can support yourself on the pay they offer. Additionally, make sure you get grade increases (i.e. promotions) written into your position description, because otherwise you are not eligible for grade increases without going through the (dysfunctional) competitive hiring process.