I am always been a big fan of using child themes on wordpress single site installs. It makes theme updates safe most of the time. But I have never tried it in a multisite install. I read somewhere that the use of child themes in a multisite install is a resource-hog and is not advisable. But on the other hand, using child themes on your multisite install does guarantee relatively safe updates of your themes without affecting any custom css on your users' sites.
Any thoughts about this?
And one more thing, would you guys recommend using on-click child theme plugin in making child themes? It seems to do the job very well and easy but I haven't really tried it.