I'd previously tried a version of Ubuntu in 64-bit, but when I installed Feisty the last time, I plumped for the 32-bit version.
I decided today that it was worth giving the 64-bit version a go and using the full potential of my processor.
I'm glad to say that everything is working wonderfully, and there is a definite difference. The main speed hike has been seen when using Google Earth - the movement of the maps are now super smooth. There is also a definite improvement in load times of large apps like OO.
Down side is that flash won't work, so I'll have to follow some instructions on how to get it working... if I can be bothered.
And... I had to find a .deb for Thunderbird 2 since it's not in the repos yet and not part of Automatix2.