problem:
since 2013.05.10, the right side widget all got big fonts.

solution:
change the style.css of TwentyTen
/WordPress/wp-content/themes/twentyten

change this:

big {
font-size: 131.25%;
}

to

big {
font-size: 110%;
}

NOTE:
you can save the main page, then open it in Mozilla HTML composer to view all the elements and their classes.