Another tip for those who are doing upgrades for customers - don't schedule the go live date until they get everything to you -- money, access to server.
I have one where the hurricane hit and the customer is down for two weeks. No way we can make their go live date this week since I haven't had any server access.
Luckily this customer is reasonable (and probably most would be in that circumstance) however some customers aren't as understanding.
Do not back yourself into a corner where the customer suddenly expects you to work nights and/or weekends to make a go live date due to delays on their part (whether preventable or not).