One of my biggest annoyances is that Gmail has not one font to use in the email body. People write with black, with blue, with Sans Serif, with Tahoma, with Arial, and the emails are looking bad all the time. Uniformity would be good in this case. It really would.
I searched userscripts.org for a solution, but could not find one that works, so I put together a Chrome/Greasemonkey script that makes all the fonts in GMail’s email body use the font Open Sans size 14px.
The script is here.