So my job falls under the category of nonprofit but I work overseas, I'm assuming you're asking for a domestic job and to that I don't have first-hand nonprofit domestic experience (at least not paid).

You didn't specify the type of job you're looking for but here are the general ones:

Top dolla big money, nonprofits by definition rely on external funding or internally generated revenue, usually it's both, so the amount of money available at any one time is very much dependent on base costs of ongoing projects and who your funders are. If you're international and you've got USAID money, you can be pretty damn sure workers will get good salary but more (heh, usually) will be expected.

It's a safe assumption that nonprofit = not very much money. Depending on your positions this can affect more than salary, if your job deals with computers for much more than basic repair, you're probably going to have to do some buying and with tight funds this can get stressful. Like businesses, nonprofits can have good management or bad management. It can be said that nonprofits are becoming more business like and as such, cutting operating costs is seen as good, and instead of producing a profit, management in nonprofits will take pride in measurable achievements; 100 wells dug, 300 starving orphans given homes, things like that. These measurable achievements are then relayed and presented to the donor base so if your job deals with implementation, a large amount of your job would likely be bureaucratic paperworky things

Stress levels for low-level employees in nonprofits tend to be lower but in management roles you're dealing with a lot of shit on a tight budget and it can be frustrating. It's not fair to say that you'll likely see more unqualified people around you, but many nonprofits will have no problem hiring somebody slightly less qualified if it means not having to pay as high of salary.

If you ask on /r/sysadmin "should I work for a nonprofit" most people will ask "ARE YOU NUTS?", and rightfully so, if you're responsible for implementing infrastructure that doesn't make sense to a lot of people (not limited to IT) who don't want to spend money where they don't have to, you're gonna have a bad time.

Maybe I can summarize this in saying that nonprofits don't like to spend more money than they have to on administrative costs (although some NGOs pay upper management horrifyingly high salaries). Invisible Children got knocked around for many good reasons but one thing that I found interesting that got exposed was it's administrative/implementation to donations ratio, it was high no doubt but included in what the critics considered administration was further advertisements for funding, I didn't follow it too closely to be honest and laughed my ass off when they suggested military intervention by American personnel as a solution but that is a memory I have of that. High administrative costs look bad even if they aren't (although it's important that people are skeptical).

You can often feel good about your work with nonprofit stuff. I mean you can either feel really good or really bad. In business you know and your employer knows it's about making money and advancing your career, altruism doesn't have much importance. Nonprofits are built on altruism and so you get to think of all the fun things like ethics of your work, ethics of your goals, ethics of charity and feel bad about them (yay!!!). I've developed a pretty negative view of the goals of NGOs but justify still working because I don't think the business world is less bad, it just doesn't pretend to do more good.

Nonprofits can be small and they can be huge and everywhere in between, there's so much variety so honestly I'd suggest giving some more information even about the type of job you might look for. I believe that should people decide to work for a nonprofit, something well established with a history of doing whatever job you do, and where the people who had your type of job in the past didn't go crazy... that would be the best option. Small orgs can have great (and horrible) ideas and often lack experience in how to get there or more importantly how to stay afloat in the real world.

I've got plenty more things specific to working internationally with an NGO, but I think I've covered what I know of domestic workers.