This weekend I installed Hardy 64 bit on my Core2Duo notebook and it flew... Just like that.
Earlier when I had gutsy for the first time on this laptop, I had plenty of issues with my hardware. Tweak here and tweak there, I had to do a lot of things to make it work the right way.
However, with Hardy this time, I would say, I felt happy for two reasons.. first it didnt complain about any of my hardware (probably because now my hardware is about a year old, and for gutsy it was so much newer..) and that its 64 bit installation.
I am yet to completely switch to this, especially since I encountered a bug with evolution and that Hardy is still beta, but I do see a way forward going with this version of Ubuntu for me.
As a result of this experiment, right now, I am triple booting, Vista business, Gutsy (32 bit) and Hardy (64 bit).
This is one thing I like so much about the PC notebooks, you can play around with them a lot more than you can do with an equivalent mac... :)
One of the guys on ubuntu forums posted this url for a better understanding of 64 bit systems... 64 bit Systems have more benefits than RAM only
Later on, I found this link, a very interesting collection of 32bit vs 64bit OS (especially Ubuntu) comparison.