This is a problem if you use Gmail to send email using another account. Outlook in particular displays your GMail account together with the email address you intend the reader to see. Here is a clever suggestion on how to avoid the problem using a Google Apps account.
Gmail’s been able to send emails from other email addresses you own for a long time, but it was never perfect. Here’s a simple step-by-step for getting rid of the all-too-annoying “on behalf of” message.