I will never go back to the days without poles. They are a great multifunction tool, between helping up and down tricky ascents/descents, acting as a tent pole, and of course, assisting with difficult water crossings. I have to agree with Mary, the vast majority of hikers you meet in the Pacific Northwest use them.
All that said, some people prefer to go without. Scott Williamson, the current PCT record holder and über-thruhiker, doesn't use trekking poles, as he said he couldn't ever get into a comfortable rhythm.
So I think borrowing a pair and seeing if they are to your liking is the best bet. A good pair will last a long time, and have replaceable tips.