You know the old parable : I've got this great ax. Had it for years. I've changed the handle 5-6 times. Only changed the head twice though. Still works great!
This also applies to computers. Corey (my desktop computer WAKE UP WAKE UP! DARLING COREY! HOW CAN YOU SLEEP SO SOUND?) started life as a Compaq Presario running WinXP. I never used the original mouse or keyboard. The heatsink clips broke, so I had to replacethe mobo, CPU and RAM. I've replaced the CD-R drive with a DVD-R. And now I've replaced the hard drive with one 100 times bigger and upgraded the OS from Fedora 5 to CentOS 5.5.
Basically all that's left of the original computer is the case and power supply.
So, do I change the computer's name? My feeling is "yes." Mainly because an OS upgrade is a large change in a computer's personality. But on the other hand, changing the might mean going through a bunch of forgotten config files and changing it here and there too. Mind you, the important ones prolly just use the IP.
But on the gripping hand, I'm lazy. And I'll get to tell the Ax Parable during cocktail parties or other inapropriate moments.