As our old friend Nik tipped us yesterday and Macworld's Jason Snell reported in his two-hour rundown of the MacBook Pro and MacBook updates, there's a stealth feature with these machines that is sure to please iPhone owners: the $29 US Apple Stereo Headset, included with the iPhone, works as a microphone on the MB/MBP unibody models.
While this might not be a top-line selling point for the laptops, it's actually a very nice added feature for users of VoIP software (Skype, Gizmo) or iChat audio conferencing. Trimming your laptop bag by skipping the USB headset (or the Bluetooth headset, for that matter) will save wear and tear on your back; not having to buy another device to do sound input for your laptop will save wear and tear on your wallet.
Update: One commenter notes that these headphones also work for sound input on the previous MacBook Pro ("MacBookPro4,1"); if anyone else can confirm, please chime in. Another asks if the clicker button works to control iTunes playback; per the Macworld article, it does indeed.
Thanks to everyone who sent this in.