I've had an Ancestry sub for years now, and love it. It's been worth it's weight in gold to me a couple of times for information!
Glenda is right. You can't consider it fact unless it's documented, however, usually one SOLID document is enough, and sometimes those are just gone. (The Union army, during the War Between the States, burned many of the courthouses and churches that held documents, and there is simply no way to document some things unless there's a family Bible out there somewhere.) Sometimes you just have to go with a preponderance of evidence, and hope that it's right.