rfung - 12:12 am on Mar 2, 2005 (gmt 0) Do it right the first time.
Not only all of the above, but there are less visible advantages to separating your content. You don't want your content about refrigerators be on the same site as your mechanical hobby robots. Eventually as you grow you end up with a mismash of information that will drive you nuts because there's no sense or organization. And then what will you do? split it into several domains.
Do it right the first time.