Not that straightforward, actually. Apple includes the Hoefler Text font in Mac OS X – its a really nice and readable professional font. Here’s what I did:

(1) You need to obtain the font in the opentype format (otf). Be careful: for me, the TTF version didn’t work. The Postscript type 1 version worked great.
(2) Use otftotfm -a to convert and install the files:

otftotfm -a -e texnansx HoeflerText-Regular.otf -fkern -fliga LY1--HoeflerText-Regular

This installs the regular form in the .texlive subdirectory of your home directory. Do this for all the font shapes you want to use. In the last step you need to create a .fd file:

\DeclareFontFamily{LY1}{HoeflerText}{}\DeclareFontShape{LY1}{HoeflerText}{m}{n}%
{ < -> LY1--HoeflerText-Regular }{}
\DeclareFontShape{LY1}{HoeflerText}{m}{it}{ < -> LY1--HoeflerText-Italic }{}
\DeclareFontShape{LY1}{HoeflerText}{m}{sl}{ < -> LY1--HoeflerText-Bold }{}
\DeclareFontShape{LY1}{HoeflerText}{b}{n}{ < -> LY1--HoeflerText-Bold }{}\DeclareFontShape{LY1}{HoeflerText}{b}{it}%
{ < -> LY1--HoeflerText-BoldItalic }{}

Put this in ~/.texlive2008/texmf-var/tex/latex/HoeflerText/LY1HoeflerText.fd. Again, make sure that all font shapes you want to use are included.

In your Latex document, put

\usepackage[LY1]{fontenc}
\renewcommand{\rmdefault}{HoeflerText}

to use the font.

The picture above was CCed on flickr by liikennevalo, thanks!