I like the idea of using a simple online service for note taking. It saves you the hassle of making backups and is available from any machine. Downside is you need connectivity. I use google docs a lot for collaborative work, its great when 2 or more people need to work on a document, real time.
For notes, I personally use tomboy (linux mono app, might be a .Net version) and then transfer to a mediawiki that I keep online for my own use. I like knowing that I have real backups and control of my data, but I do realize this isn't a solution for everyone. There are a lot of good wiki softwares out there that can be used locally for note organizing, without putting a load on your machine.
I will admit that I used onenote from MS for a six month stretch (had to with a company I was consulting), and liked it. For me, it and Visio are the only things in Office worth using.