It is OK to use as a secondary or tertiary source, as it has the potential to point to something that points to something useful. But as a primary source, it's unfortunately not very good. I tend to use things like My Heritage, Geni, Ancestry Trees, and Rootsweb as clues to help me point to the actual information that proves or disproves the facts on the profile. I wouldn't leave it off the profile if you think it helps prove your facts, but I wouldn't rely on it as a primary or sole method of doing so.