Pros
As an intern, I got to work on a technically challenging project that was crucial to the success of a real product, which doesn't always happen at all internships. My group manager and "mentor" (a more senior engineer that helped me with my project) were both very accommodating people, and I never felt awkward about asking them for help or direction. I think the culture is very, very laid back and open, which is a big plus for creating an environment that people would enjoy working in.
Cons
The pay seems to be a bit lower than other computer engineering companies. As an intern, the pay was more than enough for someone still in college, but it seems that full-time salaries are a bit lower than other top companies. I didn't really have too many bad experiences there, but it does seem that there is a lot of HR propaganda that NI is the best place to work in the world and that people are using their products to make the world a better place and all other types of idealistic jargon. However, if that's the worst thing I can say about a company, I guess that's not a bad thing.