We (@pl.wiki) have loads of reports that say "FONT SIZE IS TO SMALL!!!" (yes in capitals ;-)) and sometimes quite opposite that font size is too big. I'm aware that some reports might be made because of different renderings in different browsers (like in bug 23956), still it seems that problems like that should be resolved differently.
We try to educate people that they can zoom in/out pages in their browsers (or change DPI), but I think a more appropriate solution would be to add some "A+", "A-" buttons to make fonts bigger and smaller through JavaScript. Script could add some class to body (or #content) that would change the size and set a cookie to preserve the state (e.g. for 10 days). In e-newspapers there are usually 3 to 5 sizes of fonts. Three state version is kinda easier to do from an interface perspective as there could be 3 letters "A" with gradual size.
One more thing - we could do it with JavaScript alone, but I think the class should be added on server side so that fonts wouldn't flicker upon loading a page.
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