I don't think I have ever run into that, although that sort of thing would depend on the resolution you're using. I limit almost all of my messages to four lines in the editor, which is short enough that the game can show two messages at once in 1024x768 or above. I think this should allow for at least one message at a time in 640x480, but I have never tried it.
On a side note, the messages would be much easier to read if they didn't go across the entire length of the screen. If they were cropped halfway across for example, before going on to the next line, it would make a big difference. It is generally easier to read text arranged in short rows and several columns than in one or two long rows. This is why the text in most newspapers and magazines is set up the way it is. This would probably only be practical in 1024x768 or above, but that's what most people use these days in any case.
