I had the same problem. I use the downloaded font for my headers and on IE8, Facebook Javascript messed up the fonts. This happened when I structured my code in what I assumed was proper architecture - the inclusion of Javascript on Facebook was in my header, including the rest of my Javascript.
When I moved javascript turned on before the actual div that added a similar button, the problem disappeared.
<div id="facebooklike" style="position: absolute; left: 645px; top: -37px;"> <div id="fb-root"></div><script src="http://connect.facebook.net/en_US/all.js#xfbml=1"></script><fb:like href="http://www.tripinsurance.com" send="false" width="350" show_faces="false" font="arial"></fb:like> </div>
I think a problem can occur if the Facebook code is loaded before the div is loaded on the page.
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