The upcoming Handoff feature that allows users to seamlessly transition between workflows on their Mac and iOS device seemingly only works on Macs that support Bluetooth LE 4.0. For starters, MacRumors points out that Apple engineers during WWDC explained that the feature does in fact utilize Bluetooth LE. What's more, the recent release of the second OS X Yosemite beta includes a field for continuity support within the system information pane. The content of the field appears to be a function of which machines support Bluetooth LE
With this in mind, the website Apfeimer compiled the following chart detailing which Mac models support Bluetooth LE and, by extension, will be able to run the Handoff feature.
The red bars indicate which Mac models can run OS X Yosemite while the green bars represent which models come equipped with Bluetooth LE 4.0.
A video of the Handoff feature in action can be seen below.