It's always bugged me that Mail.app doesn't auto-detect URLs and highlight them while I'm composing a message. Sometimes I hand-type URLs, and I want to make sure I typed them correctly by clicking on them.

I discovered that if you go to the Drafts mailbox and select the message you're composing, URLs in that view of your message will be highlighted and clickable. Kind of inconvenient, but at least there's a workaround to what I consider a shortcoming of Mail. Maybe someday I'll look into creating an AppleScript for quickly opening the Drafts mailbox and selecting the message I'm editing, or if that's not possible, selecting the last message.

I submitted a bug to Apple. Its Radar number is 6269309.