Again I name Firebug as an example. There you can disable css properties by clicking directly to the left of the property. It will show a little blocked icon and grays out the property. This is such a convenient way to see what that property does with your page. But it doesn't remove it. You can easily turn it on again.
In addition I'd like to propose the same for dom nodes. Sometimes you want to turn off a node temporarily in a similar fashion as described above with properties. Very handy.
Oh, and.. as I reported earlier as a feature request (http://bugs.webkit.org/show_bug.cgi?id=16528), that summary of course must show that you disabled these properties/nodes.
Bug 14377 covers disabling CSS properties. We will use this bug to track disabling DOM nodes, a neat idea!
They can be deleted currently, but not disabled. I don't see an option to disable but not delete DOM nodes in Firebug.
Disabling nodes would be unique to Web Inspector.
This idea seems to be close enough on topic.
If you delete them, being able to undo (ctrl-z) the delete.
Being disabled would be a better option though and would probably remove the need to delete any.