@artfulrobot oh my, i spent so much time of my life deleting spaces after pressing J, thinking about doing a macro, "but really was it worth it now?" This will come in handy.
@artfulrobot gJ joins the lines and keeps existing whitespace (there may be none), gj joins the lines with a single space, I think there is no trim and join builtin
@artfulrobot I use J all the time, had no idea I could modify the behavior like this!