OneNote's "send to OneNote" printer driver has an annoying tendency to disappear without warning. The problem is that I use it far more often than my physical printer.
Apparently a the 9-Sept-08 Windows Update caused more a wholesale disappearances of the driver. See the post at Daniel Escapa's OneNote Blog. One commenter, Rainald Taesler, points out that this has been an ongoing problem since the program's launch and nobody at the ON team seems to be paying attention. Go get 'm Rainald.