I like plain text.
Although I admire beautifully typset documents, nothing beats plain text for productivity. Plain text is easy to compose, easy to send and easy to receive. Sharing/syncing plain text documents on a Mac and an iPhone/iPad with Dropbox works beautifully.
Mac OS X Apps (I set the font to Monaco 14 in all four apps)
iPhone/iPad (Courier New 14, iOS4 doesn’t have Monaco)
Cloud (for syncing and sharing)
Plain text email
Apple Mail preferences for plain text are set as follows:
Mail > Preferences… > Fonts & Colors
Mail > Preferences… > Composing
FYI, my email system closely follows that outlined by Joe Kissell in his TidBITS article ‘Achieving Email Bliss with IMAP, Gmail, and Apple Mail.’
Apple Mail messages are stored in plain text, one message per file (a modified eml format with an ‘.emlx’ extension). Apple Mail archives are stored in the mbox format which is just one big text file.
BTW, I suspect standards organizations and security folks love plain text too.