I've just recently purchased a second hand Dell GX270. Readers will note that I had Ubuntu 8.04 running on a Dell GX240 previously and I was very happy with it. Once I upgraded the RAM to 1.5GB it went very nicely. The GX270 came up at the right price so I grabbed it - a P4 with 3GHz processor, hyperthreading and all the other stuff. It's also in a slight bigger case, so I have a full sized DVD-R/RW in it as well as 2 full sized PCI slots available and best of all - 4 RAM slots on the mainboard! W00t!
Given my inherent lazines and desire to work smart, not hard I pulled the 80GB WD hard disk out of my GX240 and put it straight into the 270. I also threw some extra RAM into it to bring it up to 1.5GB and started it up.
Firstly, I had to enable restricted drivers - this new machine has an NVidia chipset and it wanted drivers. After a little bit of screwing around (basically making it re-detect the display) I have the appropriate resolution now (1680x1050). All up that took about 5 minutes. The next thing I had to do was set my static IP address which was easy and that was it. Completely different hardware, existing install and it's up and running in 10 minutes flat. From bitter experience I know Windows would have barfed on any number things - mainboard, graphics card, network card etc etc.
I'm typing this up on my new PC and it's great - happy days all around. Just another plug for how great Ubuntu is and how great Linux is in general!