Twitter provides a subtle, unobtrusive notification messages, e.g. when a direct message is sent. The confirmation appears as a layer with a white background over the top of the page, covering the page header, and unfortunately, not providing a more obvious "Close" link to dismiss the message. The message can be easily dismissed by clicking anywhere in the div, but that's not readily apparent.

1. Direct message interface.
2. Confirmation that direct message has been sent appears as layer over the top of the page.