In case you missed it, the always updating Web Apps (available at http://office.live.com and embedded all over the web) got a refresh yesterday. You can read about it more here: Announcing new features you've requested.
One of the big ones for me was that the OneNote Web App can now display ink notes. So for those of you who use the stylus a lot, your notes are now visible for you to refer to on any device.
Also check out the OneNote App for iphone, now at v 1.2 with kinks worked out, and of course WIndowsPhone 7.5 (Mango) being rolled out now has improved Office app support including OneNote. Julian Kay has a nice overview with pictures.
Don't ask me about support for more platforms: Like Sgt. Shultz, "I know nothing!"