Polyps aren't dangerous, but they can contribute to really painful sinus infections. Treatment usually involves a steroid nasal spray (nasonex, flonase etc) to shrink them down. Sometimes surgery, depending on how bad they are, but they will most likely regrow. Sometimes a combination of surgery to get rid of them quickly plus nasal spray to prevent them from regrowing is used.
Background: Broadly defined, nasal polyps are abnormal lesions that emanate from any portion of the nasal mucosa or paranasal sinuses. Polyps are an end result of varying disease processes in the nasal cavities. The most commonly discussed polyps are benign semitransparent nasal lesions (see Images 1-3) that arise from the mucosa of the nasal cavity or from 1 or more of the paranasal sinuses, often at the outflow tract of the sinuses.
From here: http://www.emedicine.com/PED/topic1550.htm
fyi; I have asthma and years ago I started developing nasal polyps. Had about 3 different surgery's for them. Then the ENT asked me if I take aspirin and I said yes. Wa-la. That was the problem. I quit using aspirin and no more nasal polyps.