An excerpt from my latest OneNote article (see this page for an index to the full series)
Microsoft OneNote has become a broadly successful personal information management and collaboration tool since its introduction in 2003. As one indication of how popular OneNote has become, a recent Microsoft blog post noted that 78 million PCs in the United States alone have OneNote installed (although it's not clear how many of those copies are actively used at this time).
However, there has been a longstanding request in the OneNote user community for Microsoft to support OneNote on non-Microsoft client platforms. The lack of OneNote clients for popular non-Microsoft platforms has been a key issue in the competitive landscape between OneNote and Evernote, a topic I discussed in my previous article ("Evernote and Microsoft OneNote: Comparing Two Noteworthy Tools/Services").
Microsoft took a big step toward addressing the request on January 18, 2011, when it announced and released a new OneNote Mobile for iPhone client. The rest of this article includes an introduction to the new client, an overview of how it may change the competitive landscape, and some comments on ways in which the OneNote Mobile for iPhone client is a hopeful leading indicator of other potential Microsoft plans for OneNote.