The font description in the mockup is (16pt, regular) https://wikia-inc.atlassian.net/secure/attachment/25228/Educational_message_Redlines.png, which is what it is in the css.  I tried font-weight:100 and it looks a little lighter in chrome and has no affect in IE10.  This UI passed a design review with Song so I think it's okay to leave it as is.