UPDATE: There is now a way to install Kubuntu in EFI mode and use binary nvidia drivers.
Follow this: http://askubuntu.com/a/613573
So I was installing the newest release of Kubuntu even before it was officially announced and hit a hard wall with it. Took me about four days to figure it out and fix it properly, so here I'm sharing it, hoping someone will find it useful when in similar troubles.
tl;dr version at the end. Somehow it turned into a full fledged story.. :D
A bit of background first. On my MacBook Pro 7,1 (mid-2011) I first installed Kubuntu 11.04. As was the custom/ritual for the past few years, with every new release of the distro I was using (starting with Fedora 5) I went to the shop, bought a CD and burned the iso. Same for Kubuntu 11.04, nothing special, everything worked. Then they decided to raise the size and not fit on the CDs anymore, so I went just with simple distro upgrade to 11.10, no clean install. Same thing with 12.04. However my root partition became a real mess with lots of devel stuff, lots of deprecated packages and libraries and whatnot. And I was constantly running out of space on that partition. So I decided to just format that partition and install the newest Kubuntu 12.10 as soon as it's out (silly me).
But since the iso no longer fits the CD, I went for installing from USB. After some initial troubles with the installer (which were partially due to bad partitioning, partially because of the installer not handling Mac's EFI properly), I managed to install it, screwing up Mac's bootloader in the process. But I didn't need it anyway, I was happy with grub and my new Linux install.
Kubuntu comes with this nice tool called "jockey", which allows you to install proprietary drivers just by clicking one button. So I went for proprietary Nvidia drivers as I play games from time to time and I use the notebook in uni quite a lot, so I need good battery life. Drivers activated, rebooting and black screen. So I did the usual - check if nouveau is blacklisted, if nvidia kmod is properly loaded, see the logs....and nothing. Everything was perfectly fine. Except the black screen. So I used jockey to switch the Nvidia driver off, rebooted and no X at all. Well since it was clean install and the install was quite fast, I just reinstalled the whole system. And same scenario happened - activated different Nvidia driver, rebooted, black. Reinstall. Tried driver from nvidia.com, no luck. Tried drivers from xorg-edgers ppa, no dice. Downgrading X server, pffft. All the same issue.
At this point I started to become desperate that I can't figure out what's wrong, Google was no help and I was without usable system for two days. Now if you're thinking - "why didn't you just stay with nouveau?" well I did. For one day, when I hit some (known, reported) bug while watching movie, sending my X to /dev/null and locking up kernel. I was starting to think that my graphics card is dieing...
Hours and hours of Googling later I found out that my system was booted using EFI mode. Investigating this deeper I discovered, that Nvidia with Linux in EFI mode are not the best friends. I learned that I needed to make Kubuntu boot in BIOS compatibility mode, basically by switching grub-efi for grub-pc. No easy task getting rid of the linux-efi bootloader though. After no luck with that, I decided to verify my theory and installed Kubuntu 11.04 from CD, which installs grub-pc and it turned out that this was indeed the issue.
So I fired up my OS X install, where the 12.10 iso was, navigated to the file, right clicked on it and it offered "Burn" menu entry. Cool, I thought and searched my entire DVD collection for an empty DVD. Found one, inserted it in, burnt, rebooted, nothing happened, DVD not detected. Desperation was doubled by now. Booted back OS X, opened the DVD and, well, when OS X says "Burn", it means "I will put this file on the disk for you", not "Burn the iso". Partially happy, partially angry, I searched for another DVD. Burnt the iso properly, rebooted, installed, activated Nvidia driver, rebooted, cried with happiness.
tl;dr - Binary Nvidia drivers are not working when you install Linux on Mac (possibly on all (U)EFI systems) from USB stick, which installs grub-efi bootloader. You need to go the old-school-last-century-way and install from CD/DVD, which installs grub-pc and boots Linux in BIOS compatibility mode. And install the bootloader to the root device, not the partition, otherwise it won't be seen by Mac's bootloader. I'm not sure if the grub-pc can be installed from the USB stick too, I really don't have any energy (and interest) left to find this out, so your safest bet is the CD/DVD, but if you have any additional info, please share in comments.