Schelly wrote on this subject, as did Chris. Now I'd like to add my two cents on the subject of genealogists vs family historians. I say the difference between the two is functional.
To my way of thinking, a genealogist is someone whose primary objective is to add (names and dates) to their family tree. They may also be interested in "putting flesh on the bones" of their ancestors but their primary goal and that which they spend most of their time and effort on is accumulating ancestors.
I think of a family historian as someone whose primary objective is to study, collect, and archive their family history with less if any concern for adding names to the family tree. They may update their family tree with new names and dates from time to time but their primary goal and that which they spend most of their time and effort on is not ancestor research. If you primarily do things such as keep and catalog family heirlooms, write family histories about your ancestors, maintain a family web site, organize family reunions, collect and publish collections of family recipes, write a family newsletter, create heritage scrapbooks, or research the lives of individuals on your family tree as opposed to adding names and dates of individuals to your family tree, you would fall into the category of what I think of as a family historian.
Back when I was actively searching records and databases in an effort to add more individuals to my family tree I thought of myself as a genealogist. I wasn't much interested in grandma's recipe for rye bread unless it was in an envelope with a return address in Poland that would be a clue to my ancestral village. Ever since I stopped actively searching for names and dates and transitioned to recording all that is my family's heritage, I've thought of myself as a family historian. My girlfriend who has never looked for a vital record in her life but who catalogs and writes about her grandparent's antiques and heirlooms is also a family historian. She is the keeper and writer of what she knows about her family's history. Her information may only go back a couple generations but it is her family's history none the less.
Certainly you might perform some of the activities I've identified for family historians while you attempt to take your family tree back another generation. Likewise you may take a moment to add the names and dates of newly married cousins to your family tree while you are engrossed in photographing and cataloging Aunt Mable's thimble collection. The key element is time. That which you spend more time at determines your label. (I spent a few minutes today washing dishes... but I don't think of myself as a dishwasher. I spent a couple of hours writing blog posts... and I do think of myself as a blogger.)
Now if you are a person who both researches ancestors for the purpose of adding them to your tree and you also spend a fairly equal amount of time recording your family heritage in one form or another, I'd say you're either a "geneahistorian", or a "familiologist". I like both terms. Geneahistorian (pronounced geena-historian) has a bit of a romantic sound to it while familiologist rings scientific. I think a good many of you functionally fall into this blended category. So tell me, which are you?