witter 0.3.4-1 uplaoded to extras-devel last night, has a first go at a portrait keyboard (I assumed Nokia was not about to drop another update with a system one in)
basically the plus button in the top bar, in landscape provides optiosn for +20, +50 etc, in portrait it brings up the portrait keyboard.
This may not be the best way to do it, but I wanted to get it in and see what it was like to use in practice.
Not all symbols are available, but I've put some of the more obviously useful ones in.