(Picture by knihm)
This is the most doubted question when there is a new version of Ubuntu or any other OS. Ubuntu 9.10 is released a week ago and it brings some improvements. There is a new version of the kernel included 2.6.31.1, Ubuntu now ships Ubuntu One by default, GRUB is now in version 2 available. But there are two things that are important to us when we are deciding about clean install or upgrade. Those features are the ext4 filesystem which is now default filesystem and the focus of the Ubuntu developers to the boot time. Ubuntu is doing great job on this, their goal is to have 10s boot time in the next 10.04 LTS release. Many of those improvements are already implemented in the 9.10 Karmic Koala. People who have measured  boot time and compared it with the boot time of Ubuntu 9.04 said that it’s nearly a half.
Almost everyone on Ubuntu forums suggested to do a clean install rather than upgrade (Clean install fiesty vs upgrade) and it was a discussion about Fiesty. If you upgrade to Karmic Koala you will not have the ext4 filesystem which is a little bit faster than old ext3 filesystem and most importantly you will not sense much of the boot time improvements.
The problem with most people is that they have much applications installed and many themes or something else installed so they will need to do that again. I’m like that myself, but upgrades have failed in some cases for me and I had to do a clean install. Now I didn’t even think about upgrade I’ve done a clean install and soon I will do a clean install of Linux Mint that I have on another partition. I first do a clean install, than install couple of applications which I use mostly and which are not included in Ubuntu. And that’s it, I will install other thing when they are needed. So install and setup time for me is 1 hours.
On the Internet, nobody can hear you fart.
Great, I never knew this, thanks.