It seems that the debate about whether there should be one or two spaces after a period continues. Thereís even a fairly entertaining video plus oodles of comments on the Microsoft site, at http://channel9.msdn.com/ShowPost.aspx?PostID=112.
Itís a publishing-industry standard to put a single space after a period at the end of a sentence. The publishing industry includes newspapers, magazines, books, and serious Web sites, like Microsoftís own. This means that when you write for one of these entities, you need to comply with their industry standard, which also includes Chicago or AP Press styles, a House Style Sheet, and probably a template.
When you are NOT writing for the publishing industry, like youíre doing your companyís technical documents or legal work or just internal documents that will not be published, you need to comply with the companyís standards. Your local editing or documentation department has a list of what those are. If thereís no standard set of rules, you can be a hero by establishing a House Style Sheet and making it available within your company. If youíre the person documenting styles, you get to say whether itís one space or two.
If youíre writing for academia, they donít care about spaces because you are doing the publishing yourself. If you need to take up lots of extra space because your paper came up short, sure, go ahead and use the extra space. But donít think your professors wonít cotton to it. Itís an old device, like triple spacing between lines and blank spaces between paragraphs.
Like double spaces, a five-space indentation was standard for beginning a paragraph. Like double spaces, the indentation is also no longer an industry standard.
Youíll find vestiges of the old indentation policyóthe first default setting of tabs in Word 2003 is still at five spaces. Some publishers use the indentation for the first paragraph of a book or an article, but all the rest are left justified. Donít do this first indentation yourself, though. The publisher has a process for doing that automatically.
I suspect that, like the double spaces, the ease with which word processors adapt to accommodate the font style has eliminated the need for the old indentation. With some publishers, youíll find that they want a blank line between paragraphs, which would render the indentation a needlessly wasteful of space.
The bottom line, folks, is that it doesnít really matter what you think is appropriate. It matters what the standards of your publisher are.