When you roll out changes to a live web site, how do you go about checking that the live system is working correctly? Which tools do you use? Who does it? Do you block access to the site for the testing period? What amount of downtime is acceptable?
I tend to do all of my testing in another environment (not the live one!). This allows me to push the updates to the live site knowing that the code should be working ok, and I just do sanity testing on the live data - make sure I didn't forget a file somewhere, or had something weird go wrong.
So proper testing in a testing or staging environment, then just trivial sanity checking. No need for downtime.