I have only done it on my test system and it survived. So, when I get some time to stay late - I will do the upgrade. The problem is people like to work like 2 or 3 hours past closing... and I get grief if I tell them phone system will be down for 15 or 30 minutes for update. The "stay laters" are often dealing with their international clients at this time.
The actual upgrade is one or two minutes only, after downloading SP3, not 15 or 30 minutes.
It will be nice if you could schedule it later or when system is idle.