I use EMACS for the vast majority of editing, but the support for word wrapping has always been a bit of an annoyance. Especially when writing stuff to go into web forms. By default, the only way to wrap words so that lines don't run off the edge of the end of the window is to use auto-fill-mode, which inserts newline characters at the end of the lines. This is exactly what is required for text files that are expected to be read with dumb pagers like less or more, but it can result in erroneous line breaks in things like web forms. An additional annoyance is that auto-fill-mode only inserts line breaks automatically when the cursor reaches the end of the line, so if you go back and edit in the middle of a line, you have to type M-q to get the line breaks back into the right place.
Enter LongLines mode. LongLines solves both of these problems by automatically inserting newlines where ever they may be required for word wrapping, but strips them out when saving or copying, so you don't see extra newlines in your forum posts.
yay!