They would not work because no mobile browser would support the contentEditable attribute despite the fact that all the major browsers support it in their desktop versions - Internet Explorer since 5.5. Well it seems Apple have been listening and now these things will work in IOS5. Great if you have an iPad 2.
Not so great with Android though, which not only still fails to support it, but actually lies if you test for support:
returns "true" but the onscreen keyboard will not appear so you cannot type into the edit area. This is Issue 8253 for Android. No sign of a fix yet.