Running ubuntu as my main OS on my 2011 MBP for a while. Everything works and is stable except for the wireless driver, which you have to compile yourself and only supports wireless G. Things may have changed in the last months though. I don't know about the 2009 MBP hardware.

I've been running 11.04 on my 2010 MBP for a while. It drains the battery pretty quickly. I had to mess around with the trackpad settings a bit to get that into a usable state, and I had to disable tap-to-click completely because it completely sucks at palm rejection. The startup screen is completely screwy and it often fails to turn the machine off when shutting down.

Triple booting on Santa Rosa 2007 MBP. Upgraded to Lion from Snow Leopard and had many problems, lack of recovery partition, Spotlight failure etc. Need to reformat and reinstall all to get spotlight working again.

Ubuntu is now my main OS.

I had severe difficulty getting Ubuntu to appear as a bootable partition when installed from a USB stick. Don't install from stick, install from a disc. Whatever it did with EFI didn't work right, there were partitions on my hard drive that Mac OS X wouldn't touch, it was a mess.

I had to repartition and reformat my HD and restore from Time Machine.

I recommend using rEFIt: http://refit.sourceforge.net/

It can help with some of the multi-boot problems people tend to have with Ubuntu on MBP.