I've been using OneNote to organize my campaign, and once we got the format down, it's worked very well. I have a passworded DM tab and a Player tab. I use the DM tab to organize my notes, outlines, put in photos, art clips, maps, etc. My players use the Player tab to collectively take notes, track treasure, quests, etc. Because everyone can work in the document at the same time, it's a great resource for collaboration. I can run it off my iPhone, ipad, or laptop.
One downside that was mentioned above is having to switch windows. At first it was indeed a little slow, but now it's just switching windows. It's no different than shuffling papers or flipping through a notebook, looking for the one page you need. A little faster in fact, because my tabs are named.
One thing I've also done is plug my laptop into a large TV or video monitor (we play in an office conference room), which allows me to share art and maps with my players. By "extending my desktop" onto the TV, I can drag over maps or pictures of NPCs, scenery, treasure items, etc for everyone to reference. I only started doing it a few months ago, and it's been universally thumbs-upped by my players.