Install OS X 10.10 Yosemite in VirtualBox
Due to the high usage of this guide and the lack of comfort in Gist's commenting area, I decided to make a blog post out of this which you can find here:
http://blog.frd.mn/install-os-x-10-10-yosemite-in-virtualbox/
FYI, I just downloaded yosemite today to try this and after the iesd step, the resulting yosemite.dmg already has both BaseSystem.dmg and BaseSystem.checklist. I think you can remove all the steps regarding creating a sparse image, copying the files, and then recreating the dmg saving many gigs of extra copies.