I really haven't worked in the Apple ecosystem, before this I had an Apple iPod Nano 2G years and years ago and that was the first time since elementary I'd touched an Apple device - and those were the ol' green screens. However I figured that a. getting a Hackintosh working would be fun, but also that it'd probably be a good thing to say that I could work in a 'technical' sense with OS X.
And boy, was it a challenge getting Yosemite working on this laptop. It all started with the fact that /I didn't have access to OSX/. I bought from the Apple Store Mountain Lion, thinking I'd be in some way able to directly download it and put it on a disk. To me this makes sense because what if something happened to your Mac and you can't access it and you need to reinstall? Well, no. You can't do that. Luckily there are a few iMacs at my University and I was able to download it on there.
However Mountain Lion is 10.8, its a few years old and definitely not what I wanted. So I stuck the sucker with some hacking and slashing into VMWARE and from /there/ downloaded the image for Yosemite. At this point the wonderful guides at TonyMacx86 without whom none of this would be possible.
So in order, from the moment you have a Yosemite Image downloaded from the AppStore. Basically just follow this guide and you'll be fine, I'll just make notes of differences that have to be done for the x240.
1. Use Chimera to create a boot disk.
2. Make sure secure boot is disabled and you can boot from /both/ gpt and mbr disks.
3. Load up Chimera, and go through the install.
a. You need to install it on its own drive, there can be no other partitions.
b. The Installer might have issues so while on the Yosemite symbol in Chimera type "-x -no-zp -maxmem=4096". This will make it so it doesn't look for zone poisoning for allocating memory, and then tell that it has only 4GB of Ram.
4. The installation should work fine, go through it and install as you want.
5. I installed Clover as my boot manager for the following fixes. Start from step 4.
6. I had to install the Mobile Intel 4400 kext fixes to fix graphic corruption and instability.
With that, I have a working Mac OS X 10.10 Yosemite on my x240. For your information my specifications are an i5-4300U/8GB/Intel4400/1TB.
At this time the only thing I don't have working is multitouch gestures on the touchpad and hibernation, both of which are very difficult to get working apparently. I had to buy a USB Wifi dongle, the TP-Link TL-WN725N works fine with the third party utilities. This entire thing took me over a week to get working, and only now is about done, however I have started to forget steps - hence the lack of detail.