I thought I would add that I have just completed a successful HP ProBook 640 G1 install of Yosemite 10.10.2 (as of 25 Feb 2015) using the Yosemite with Clover
guide.
The HP ProBook Installer now also includes an option specifically for 6x0 G1 laptops, so no confusion there.
I swapped the Wi-Fi card out for the
BroadCom BCM94322HM8L BCM4322 Half Size Mini PCIE WIFI Wireless Card for a pifling £8.50, which worked without any extra jiggery-pokery - very pleased with that, as I had an Edimax dongle which did work, but the software was so poor it wouldn't remember the network password,
I cannot attest to the display port or VGA out or even the audio jack issues that some of you have been having. I simply needed a Hackintosh for InDesign for my wife, as some older fonts were simply not playing ball with Windows. If I were confident enough to dual boot it with Windows, I would, as it's not a half-bad gaming laptop!
I did run into trouble the first time I used the HP ProBook Installer as I ended up stuck on the UDID line on boot, but that was owing to me too hastily selecting the wrong options. Tried again and all was well.
Thanks to Rehabman for all his comments throughout many threads that helped me get there in the end.