How many Windows users have downloaded the Safari 3 beta, took one look and said: “Ugh! The fonts look all messed up.”?
Well, for Mac users the same can be said when looking at Windows applications. And especially those irritating underlined letters that are meant to give a hint to keyboard shortcuts. They have sneaked into some Mac programs too, usually PC or Linux originated ones such as NeoOffice.
The reason for both the fuzzy letters and underlines is simply the different directions Apple and Microsoft take on such matters. Apple have chosen to follow the path of making letters display on screen as true to reality as possible. Microsoft prefer to optimise the letters to the nearest pixel and so distort some of them. For that reason I look at PC screens and say: “Ugh! The fonts look all distorted”.
Bitmaps first
Apple’s choices as far as the fonts go is probably a legacy of their strong showing amongst graphic designers. It has always been possible to lay out a page in a Mac design program and see as near as possible what the finished printed article will look like. In the good old days of the last century this was achieved by having screen fonts of bitmaps at various different sizes for QuickDraw to select depending on the screen’s magnification.
ATM
Then in 1991 Adobe released their Type Manager, a free System Extension that used only one of the bitmapped fonts to render Type 1 PostScript fonts on-screen. This was in response to Apple’s new outline font system called TrueType, which they had also licensed to Microsoft in return for TrueImage, a Postscript compatible printer driver. This was never used as Apple renewed agreements with Adobe for the use of PostScript in its printers following a whinging speech by Adobe’s John Warnock who accused them both of selling snake oil. Apple and Microsoft continued to develop TrueType in competition with PostScript and eventually Adobe joined in so that today Open TrueType, aka OpenType, has support for Adobe’s Type 1 fonts.
Adobe also developed Display PostScript which Next, IBM and SGi adopted for their workstations. When Apple bought Next they chose not to use Display PostScript for licensing reasons, instead using Adobe’s free PDF standard and Apple’s own Quartz technology.
TrueType
TrueType contains many ‘hints’, an Apple patented feature that helps to make fonts display their letter shapes more reliably, along with anti-aliasing which smoothes the edges of fonts on screen, making them slightly blurred. In MacOS X, Apple have abandoned using the hints although Microsoft’s ClearType font rendering mechanism still does. ClearType additionally uses the pixel structure of LCD screens to increase the apparent resolution of text but at the expense of altering the shape of letters to make them fit the pixels.

Which is best?
It’s down to personal preference. See above. On the left is the page displayed on a PC, centre is Firefox Mac and right Safari Mac. (Thanks to Crosby! for PC screenshots). As the image demonstrates quite clearly, Safari’s screen is much easier to read. I find the Windows screen almost illegible and Firefox a sort of halfway house.
To my eyes, Microsoft fonts look ‘wrong’ and I find them slightly irritating as a result. I think Apple’s fonts are easier to read and choose to use Safari as my default browser because it gives the best overall display compared with Firefox, et al.
In any case, the matter is moot as screen resolutions increase, the amount that both font rendering technologies alter the display of fonts will decrease.