AP Style says to treat an ellipse as one word by using 3 periods (dots) with a space on each side.
This sentence ... with an ellipsis.
This is for journalism and based on what looks proper in that medium. Without any spaces, an ellipsis is considered "one word" by many computer systems and therefore will not be split up properly at the end of a line. The space before and after ensures that there isn't a huge word wrap if both words and the ellipsis were all treated as a single word and dropped together to the next line. No spaces in between the periods ensures that the ellipsis won't get word wrapped in the middle of the punctuation.
The Chicago Manual of style says to use three spaced periods. This is based on punctuational accuracy and would be considered the "real" way to use an ellipsis in a grammar bar fight (if there were such a thing.)
This sentence . . . with an ellipsis.
The most important thing, is that virtually everyone in publishing says do NOT use the special "ellipsis character." Microsoft Word uses it to "auto-correct" your work by default. (While we are at it, you should also not use smart quotes either.)
It's all an interesting theoretical discussion, but in the real world of fiction publishing, here is how it breaks down.
- Your unsolicited manuscript can use ellipsis with or without spaces and it will not matter to the agent or publisher you send it to.
- Once you are actually working with the publisher, they will give you very specific formatting guidelines for how they want your submissions to be done for everything you send to them. These guidelines will encompass much more than just how to type ellipsis, and they will be the only rules that matter when submitting to that particular publisher.
You can look up the manuscript format submission guidelines for individual publishers, but you will find that most of them don't say anything about ellipsis. That isn't an omission; they don't care.
As far as how an ellipsis comes out when printed in hard copy, that is entirely dictated by the font and typeset used by the printing company, so it doesn't help to look in published books for examples of how to type it into the computer (or on the typewriter :)