Danw12321 asked the Answer Line forum if it's okay to work while Windows Update is updating Windows.
Windows Update explicitly says that you can go on working while updating. I do it, and have yet to run into problems I could connect to this habit. The simple truth is that the serious part of the update, where your system files are changed, happens later with the reboot.
Which isn't to say that there aren't some jobs you should probably avoid at that time. Defragging isn't a good idea while an update is going on. I'd also avoid installing or uninstalling an application.
The worst part of the update experience (assuming the update itself doesn't do more harm than good), is the message popping up asking for a reboot. Luckily, you can put off the actual reboot until it's convenient for you.
Read the original forum discussion.