17. may, do you mean what I will do that day this year or what is normal?
People go in parades and eat ice cream, hot dogs etc. It is above all a childrens day. Women dress in national costumes, which vary from region to region. Men fashion is suit, allthough the latest trend is also for men to cash out a 50.000 NOK handmade national costume.
College graduates terminate a long period of heavy partying, called "russetiden" on this day. After the main parades, which usually take place before noon, the "russ" have their own parade, mainly a competition to expose their large party busses which share loud Ibiza party music to the audience. A group of college graduates may spend up to 1 mill NOK on this project, which only last a few weeks prior to 17. may. A few days later they have their final and desicive exams...
Socialists in the capital arrange their own version because they find the traditional flag-waving thing too offending to newcomers in the country (which on this day sell gaz-baloons and kebabs for millions to the natives ) and themselwes . It would be like having St. Patrics day in an open park area with rock conserts, punk people and anti racist appeals.
Family people watch the main parade where schools march through the streets, or take part in it themselves. Afterwards most people either go home to their gardens and barbecue or go to the local pub and drink the shit out of themselwes, not very unlike the celtic approach to a national day.
Some hard core ski fundametalists celebrate the day enjoying the last snow in the moutains. As for many Norwegians skiing and the wild mountain landscape are the greatest symbols of national identity.
Asylumn-seekers on round-trip and groups of people from Poland celebrate the day by having a pickpocket party.
All this is broadcasted live from the old state tv-channel NRK.