Real "Vanity" publishing outfits (Trafford, Dorrance, Vantage, etc.) depend purely on up-front charges by authors for producing X copies of a book, with no significant attempts at distribution. They are nothing more than very expensive printers. Very few bookstores will even look at a title produced through them.
Some other "self"- publishing outfits are quite legit, notably Lulu. They don't pretend to be anything but a printer, with a few optional frills, should you want those. At base, they cost nothing up-front, and make their profit off individual book sales, either to, or by, authors. They are an excellent choice for niche books, like club handbooks, family histories, class manuals & materials, etc. I know (not personally) of one Civil War buff who has reproduced a bunch of out-of-copyright memoirs, histories, etc., related to that, in a very nice format. I purchased another historical account of an exploration through New Guinea via a Lulu author, and found it quite good. But don't expect to hit the NY Times bestseller list via this method.
And we have an entire set of massive threads about PublishAmerica here, so no further comment is required about them.
caw