Boy, It's been like 15 years since I last read Computer World Magazine. I use to love computing back in the 90's.
In all my years, I've never seen a corporate network upgrade that has occurred without a few hiccups. Proper planning will mitigate such problems and can even result in the end user not noticing anything.
At home in the UK, I have my own server (cause I am a nerdy bastard), once, when upgrading I managed to drop a blade server on my foot nearly breaking my foot... Server was okay, my foot near feel off though :P.
Anyway, I am rambling. Glad to see that you're well and thanks for the dose of nostalgia
RE: Upgrades without downtime: Here's how it can be done