The only thing id want in portrait mode is the messaging app, yes we could stop walking for 2 mins to reply but what if your other hand is busy? Like walking the dog, holding shopping bags etc etc, in apps like this (apps that require alot of text input) should allow the user to have both modes to use at will, its not a show stopper but we have been using mobile devices with portrait orientation to text for years, why change it now? What if your chating via IM? You dont want to stop walking to use both hands every 30 seconds etc just to reply.