I have a MacBook Pro 5,2 model, one of the last 17 inch models. A few months ago, I did a clean install of 12.04 (no OS X). I upgraded to 12.10 yesterday, and everything is going well. I did have to take about three days to get my install working perfectly. This is a good weekend project.
Make sure to do a complete backup of all of your data on a separate drive. I recommend a complete byte-for-byte drive copy. I cannot stress enough how important this step is. After a clean install, you will need to copy all of your files over to your Ubuntu install.
There were a few problems that I had to get through first, however. Heat wasn't exactly an issue, since your fans will make sure that your CPU doesn't melt. However, without a special program installed, your fans will always run at max RPM, which is quite annoying and unnecessary. You want this program to control your fans:
macfanctld - Fan control daemon for MacBook
You will also want to add this repo for mac-related stuff in Ubuntu:
sudo add-apt-repository ppa:mpodroid/mactel
You also might have some problems with WiFi drivers. If you do an install, make sure you have (1) power and (2) wired ethernet. On 12.04 I had to custom install some Broadcom drivers for WiFi to work properly. However, in 12.10, Ubuntu's Install Drivers thing works for me (Software Sources -> Additional Drivers (tab)). Make sure to install the Broadcom Corporation wireless drivers.
You will also want to install the current Nvidia proprietary drivers.
I did a good deal of web searching during / immediately after my install. These are a collection of websites that I used when doing my install. They might not be applicable for your situation, but I recommend that you do a read through to become aquainted with what others have done.
Good luck with everything. I know that I am 100% glad that I made the jump to Ubuntu full-time.