It would not be that hard if you had a keyboard attachment for the 360 controller
Because everyone wants to hold a controller, bulked up with a lousy keyboard, with small keys, to try and write down notes constantly.
As said before, best idea is seriously, just keep a notebook. You can't rely on a videogame to let you do everything. We saw what happened when that was tried (Prototype) and it turned into the most repetative thing ever. The important notes you need to know are kept in the pipboy. If you need other stuff, get a pen and paper.