There seems to be a small problem with many websites viewed in the latest version of Chrome on OS X as of recently (version 22.0.1229.79, updated on September 26, 2012).
The issue, documented here on the chromium issues tracker, talks about the fonts looking slightly more bold, or heavier, thicker and sometimes fuzzy due to a small repair job done on CSS -webkit-font-smoothing property that many web designers and developers were using to make their custom web-font typefaces render as intended by the glyph outlines in the fonts that they embedded on their websites.
firstname.lastname@example.org reports that the bug where it also affected the weight of the text as a side effect has been fixed.
He also mentions that the additional weight of the typeface is rendered on purpose by the CoreGraphics API on OS X. There is a setting on the system that smooths text for LCD monitors, dialating the glyph outline by a factor of two, and that there was in fact a bug with the previous -webkit-font-smoothing: antialiased CSS property that ignored the CoreGraphics doubling of the dilation effect and rendered the font to its intended outlines without any smoothing.
Now that the bug has been fixed in Chrome's code, the antialiasing bug is no longer dismissing the CoreGraphics LCD smoothing and therefor the fonts look heavier.
There isn't a straightforward solution to fix the bolding of type on webkit browsers on OS X, however one might try addressing Apple OS X's CoreGraphics LCD font smoothing directly by turning off your system's LCD smoothing in System Preferences (under Appearance or General Settings), or with the following command in Terminal and restarting your browser.
defaults -currentHost write -globalDomain AppleFontSmoothing -int 0
The default when using lcd smoothed text is 2. To reset to the default value, use this command:
defaults -currentHost write -globalDomain AppleFontSmoothing -int 2
Note: This won't modify the way your website is viewed on other people's computers with OS X and webkit-based browsers. This only affects your ownlocal OS X system LCD font smoothing rendering.
Update: apparently the Chrome team is going to revert the fix to a planned bug so that they can buy themselves time to release a proper solution.