It would be nice to see the how the merge fields in an email will turn out by previewing the email using a specific constituent's record, or the actual constituent records in the associated mailing list, the way you can when creating a Microsoft merge document.

When you send a test email with merge fields in it, all that comes through is the name of the merge field. The only way to see what it will look like is to send the actual message to a test record in RE. Then it becomes one of your officially sent emails that affects your results and stats, and you have to make a copy of it in order to keep editing it.