OneNote 2010 Default Font will not change what appears in the document

Mention the type of user account you are using? Is it a Standard or Administrator type account?

Changing the Font in the Basic Text group under Home tab will not change the default Font in OneNote. To change the default Font used in OneNote goto File, Options and General.

If you have already tried the above steps and failed to set the new Font as default, then repair Office 2010 installation and check how it works.

http://office.microsoft.com/en-au/project-help/repair-or-remove-office-2010-HA010357402.aspx#_Toc269981340

If you are trying to edit a list or notes that was already created using Calibri font, then changing the OneNote default font would not work unless the font of the list is changed manually (by highlighting the content and changing it). Changing the default font only works for the new Paragraphs, Sections, and Notebooks...Etc.

You may also refer to the following thread which discusses a similar issue and check if it helps:

http://answers.microsoft.com/en-us/office/forum/office_2010-onenote/how-can-i-set-the-default-font-and-type-size-in/9f972308-1393-4190-917f-e64f6d446893

http://answers.microsoft.com/en-us/office/forum/office_2007-onenote/default-font-in-one-note/19b71845-27e4-434c-b6ad-90a0f831f3f9