It appears that Apple is spending at least a few dollars out of that US$51 billion cache of cash. 9to5Mac reports that the company has purchased a small Bay Area Bluetooth headset design firm named Wi-Gear. Wi-Gear's products included three generations of the iMuffs A2DP Bluetooth stereo headset (seen above), which worked with a rather unsightly dongle for those devices that didn't have built-in support for Bluetooth 2.0 and without the dongle for newer iDevices.
The story posits that Apple picked up Wi-Gear to design an as-yet-unannounced stereo headphone product for iOS devices and MacBooks. Apple's previous foray into this market was the highly unsuccessful mono Bluetooth headset, so it appears that the company decided to just buy the expertise needed to field a competitive product.
One of the co-founders of Wi-Gear, MIchael Kim, now lists his current position on LinkedIn as an iOS Bluetooth Engineer at Apple. The About page on Wi-Gear's website now shows the following message: "Notice: Wi-Gear has ceased operations and is no longer in business. We will be unable to respond to any inquiries."
9to5Mac seems pretty certain that the end result of the acquisition will be a new Apple-branded stereo Bluetooth headset. I'm personally hoping that Apple lets Kim and the other Bluetooth Engineers design the internals, and gives the external design to Jony Ive's team.