Macs that hate Adobe fonts, love Microsoft ones
According to the article, "Keynote may unexpectedly quit when using specific fonts on your Mac OS 10.5 (Leopard) system. This unexpected behavior will most likely occur when adding a build to text ..." The fonts in question are Courier Oblique, Courier Bold Oblique, Helvetica Oblique and Helvetica Bold Oblique.
These fonts are part of the Adobe Courier and Helvetica typefaces found in the original LaserWriter's PostScript interpreter and have shipped as system standard fonts in all Macs since that time. I use Courier as my standard font when writing.
Apple says that the solution is to use the Courier New and Helvetica New versions of the font instead, which will "return correct behavior." Say it ain't so!
The "New" versions of Courier and Helvetica were introduced by Microsoft way back in the first editions of Windows. Courier New was the monospaced standard font in Windows until the release of Windows Vista, which introduced Consolas, one of 6 new ClearType fonts that all start with the letter "C."
Mac users have mostly disdained Courier New, which was seen as weak and spindly compared with the proud and sturdy Courier version. In a bit of a search around the Web, I found that even Windows programmers hated Courier New and looked for fonts that were the "most Mac-like," meaning plain ol' Courier.
One fond memory of Courier was how Postscript interpreters would substitute it for a missing typeface. This was back in the days when we used screen fonts (for writing to the screen) and Postscript type libraries for hardcopy. Suddenly, your beautiful 60-point copy was turned into a monospaced mess. Lovely.
Perhaps this rejection of a Classic Mac font by Keynote and OS X is yet another sign of OS X bowing a bit to the dominant Windows platform. I note that the iPhone's font list uses Courier New as well.