Change the default font in Illustrator

A super easy way to say goodbye to Myriad and hello to your favorite font!

1. Quit Illustrator.
2. In the Adobe Illustrator [your version] /Plug-ins folder, copy the current default startup file--Adobe Illustrator Startup_CMYK or Adobe Illustrator Startup_RGB--and save it with a different name. (This creates a copy of the original startup file in case you need it again.)
3. Open one of the default startup files (Adobe Illustrator Startup_CMYK or Adobe Illustrator Startup_RGB, depending on which type of document you intend to use).
4. Choose Window > Type > Character Styles.
5. Select the Normal Character Style and choose Character Style Options from the palette menu.
6. Select Basic Character Formats and choose the desired font from the Font Family menu.
7. Click OK, and save the new file as Adobe Illustrator Startup _CMYK or Adobe Illustrator Startup_RGB in the Plug-ins folder.
8. Restart Illustrator.

Support article source: http://www.adobe.com/support/techdocs/322398.html