Seth Godin’s e-mail checklist is good advice for anyone writing business-related e-mail. One of my favorite points is #31:

If this email is to someone like Seth, did I check to make sure I know the difference between its and it’s? Just wondering.

‘Net shorthand is not legitimate for professional communication, and knowing the difference between common nuances like “its” and “it’s” lets the recipient know that you are an intelligent being. And while you’re at it, be sure you are making proper use of “their”, “there”, and “they’re”.

Link via Ma.tt.