I posted a detailed guide on my blog about how to create a Yosemite VM, feel free to check it out if you're interested. Graphics are still slow (and it's even worse in Yosemite) but besides the login screen which takes a good 5 seconds to render due to its transparency, everything else is pretty usable, and it's enough for occasional (hobby) iOS development until you get enough experience to make profitable apps in which case it's still better to buy a real Mac as this setup may break at any update. This will improve the video playback on the applications that you run on the virtual machine. An SSD is a must have though, a hard drive will be bloody slow (that's also true for a real Mac). When trying to run videos and other graphics heavy stuff, if you see VirtualBox running slow, there is a possibility that you may be able to solve it by allocating more video memory to the virtual machine. In the end, with my solution I am able to successfully run Yosemite with 3,5GB of RAM (out of the 4GBs of my computer, and by tweaking the host system I could probably push it even more to 3,7GB), using the two cores of my CPU, with reliable USB pass through and no tweaking required (the emulated hardware is close enough to a real Mac that the OS boots directly without any kernel command line parameters or extra kexts). Answer: VirtualBox is a Virtual Machine emulator - it emulates (virtualises) computer hardware to allow you to run an Operating System (OS) in a virtual environment, running on top of another (host) OS running on real hardware. All these performance problems stem from the fact that it emulates an ARM processor so it can run the actual code of your application.

What you can do (and I have done it with much success) is use a lightweight Linux installation as a base for QEMU which is a Virtualbox alternative, with much more configuration options, including the ability to emulate the Apple SMC and its 'OSK' string (you won't need shady 'hackintosh' kexts) and it has reliable USB pass through (I successfully restored iOS devices and installed apps on them). I have finally successfully managed to install Mac OS X in a virtual machine on my Windows 7 laptop using VirtualBox and a tutorial from Lifehacker. Finally - the emulator launches, only to show how slow it actually is. Virtualbox on Windows is definitely not suitable for this, as Windows itself is quite resource-hungry, Virtualbox lacks many configuration options and even if you can get it to work it's going to be quite unreliable, not to mention that you can't pass through USB devices.

Virtualbox mac emulator slow