Edited: I messed up the value name
While I’m probably a Luddite, I prefer to read my mail as plain text. However, Outlook 2007 removed the option to set that in the Reading Pane. Poking around a bit, I found if you add a DWORD value, ReadAsPlain, and set the value to 1 in HCKUSoftwareMicrosoftOffice12.0OutlookOptionsMail, you’ll get the plain text glory. If you do want to see a mail from someone who’s using HTML format, you can click on the convert bar at the top of the window to switch the view of that mail back to HTML.