Cocoa Grey Message Overlay
Various applications on Mac OS X display messages in a grey, transparent, rounded box overlay to notify the user of something; for example the "Build Succeeded" message in Xcode, the looped search message in the Lion inline-search bar and Chrome's "Warn Before Quitting" message.
An example of the message box I'm describing: http://2.bp.blogspot.com/-eG890NRhQbs/Ty0vLkqpBWI/AAAAAAAAAMs/PO2EbJ3lTs0/s1600/Xcode-11.png
As they're all very similar in formatting, it makes sense to assume there are some sort of standard functions for displaying a similar message. How can I have such an effect in my own Cocoa application?
There isn't a public system API to do them.
You could have a look at Matt Gemmell's version: scroll down to RoundedFloatingPanel on this page.
Alternatively, if you want to Google for others, they're often known as Bezels. The private framework that draws the system ones is BezelServices.