Google's reading my letters! :-)

Cute, but disconcerting message from gmail

A bit scary. This popped up for the first time today :-)

Update:20091014.  Silly me.  I turned it on. It's a Gmail Labs feature:

Forgotten Attachment Detector

by Jonathan K

Prevents you from accidentally sending messages without the relevant attachments. Prompts you if you mention attaching a file, but forgot to do so.

Scary message while composing Google mail