If the cell width is too short, Excel either simply cuts the visible text off, or it flows into the next cell (depening if the next cell has some content in it or not).
Excel displays ### when the cell content contains just text and it exceeds 256 characters and the cell format is set to "Text". Usually, setting the cell format to "General" fixes this problem.
However! If you use this cell as a data-input to, for example, a field in a merged Word document, only the first 256 characters will be grabbed!!!
I have not found a fix for this as of yet, but would like to know a solution for the later problem.