I'd be more interested in the other half of the question. How will you prepare for your upgrade?

Places I've seen have no testing methodology for their LOB applications and basically "start it up, and if things appear to run, stick it in development, and if it doesn't fall over, give it to your smallest client, and if they don't die, deploy it to the rest."

I think you are MEANT to do a full backup, begin a trace to record a day of work, take another backup, and then use replays to compare the end results. Right? But, not many people appear to have gone into depth with examples of how to do the "best practice"... so few do it.