A lot of people get away without knowing scales, but many of them are the people that learn Stairway to Heaven or the intros to some other songs and play them over and over and over or perhaps a couple chords (G, C, D) and bang away at them. Knowing your scales and chords (chords come from scales) will help you write music, improvise, and understand what the hell people are talking about when they say, "Wasn't that cool when Vai played the Dorian mode in that passage in 'Tender Surrender'?".

All you need to worry about at first is the major and minor scales. That'll get you through the bulk of scalar theory. Move on to modes when you have the major and minor scales totally down (and you'll notice that you'll have two modes, Ionian and Aeolian down too, when you start the modes). Once again, it's not necessary to know the scales, but they'll make you a MUCH better player in the long run.