Even more important: Windows uses _very_ aggressive hinting for its default fonts, especially the new set introduced with Office 2007 and Windows Vista (Calibri, Cambria, Consolas). Though I very much like the effect for my programming font (Consolas is great in that respect), it destroys the scalability of a font to a very high degree (this is the reason why zooming a Webpage in any Browser reflows your text, and why some fonts look different in shape and/or height/width ratio in different zoom-levels; beside that rendering-engines decision to round the font-sizes to the next full pixel).

IE9 promises to not do this anymore, and on high-density displays (the better smartphone ones) it is simply not needed.

So the problem is two-fold: a very distinctive look of Microsoft fonts, and a sub-optimal fallback for non-aggressively hinted fonts in Windows.

However, if one uses font-sizes that one can actually read (for instance, bigger then 12pt, thank you all very much) the pixel-per-character count gets big enough that the results start looking better -- especially as the user does not unconsciously move his nose to meet the display in person.