I think the instructions I followed were actually for 11.10 originally. For a desktop system you don't need to muck about with device nodes and such they're already there, just install the driver and you should be good. Install the driver, reboot and you should be ok. If it complains about the Nouveau driver the nVidia driver can put that in the black list but you'll need to get to the recovery console to get the nVidia driver installed afterwards which means getting to the grub menu. To do that you need to keep quickly tapping the left shift key as the machine boots, and I really do mean you have to keep doing it and do it QUICKLY. This menu is a bugger to get into. Once you're in the Grub menu, select the "recovery" option for the kernel you're using (VERY important to pick the right one, it should be the first recovery option from the top of the list) and when you get to the next menu pick the root terminal (very bottom) option.
You will now be in a terminal, don't even think about trying to start a desktop session or this won't work.
cd to the directory where you saved the nvidia driver and run it ( ./NVIDIA<blah blah blah>.run ) It will complain about being started in this mode but just go through it and answer all the questions. Once it's done type "exit" to get back to the last menu and then select "boot normally". That should be it done. If the driver is running then BOINC will see the CUDA/OpenCL device.