Well I have had a couple people come to me with messy problems of disabling buttons as well as tabbing of lower levels in their "systems" Well I thought it was a known feature but 2 people in 2 days means I better spread the word :).
Essentially setting someMc.enabled = false; will stop input from someMc and all its children. The same is with tabEnabled (I can't recall you may have to turn tabChildren to false as well but I don't think so)
Both these people are working on systems with modal abilities (popups) and this is where these came in handy for them. When working on "OS" type projects I tend to have a holder mc for each "layer" ie. Application, Contextual, Error...and that way when Contextual pops up all I do is Application.enabled = Application.tabEnabled = false; and wallah.
Check out EricD's post.