I have done it before, sticking with email, however I think it goes against the spirit of the game in most cases. I can’t explain really why I feel that way, but I just do. Maybe I feel this way because the ease at which people check their emails is almost as simple as checking the time on their watch, where the game was intended to be played infrequently throughout the day. Just seems wrong.
One thing I do using the in-game messaging is I post screenshot links to imgur sometimes. I think utilizing tools like that is okay in most cases.