Gmail Error Proofing for Attachments. I don't know if this is a new Gmail feature, or if I just discovered it, but there's some nice error proofing built into the web-based mail application. If it detects the word "attached" in an email body, but there's not a file attached, it gives you this pop up message.

This is similar to the the method for error proofing Outlook that I wrote about earlier.