I thankfully learnt early to question what other people publish when I found a family tree containing the name of my 3x great grandmother. They seemed to have family members all the way back to 1500, which I found impressive but by no means extraordinary enough to make me immediately wary. However, once I had a closer look the flaws seemed obvious:
1) People seemed to zip from one end of the county to the other, which given it's Lincolnshire, that's a fair distance. Not a terrible problem, but it needs to be backed up and this wasn't.
2) Despite all their searching over hundreds of years and the entire county, they failed to find that my 3x great grandmother had married. Sure, it didn't all happen in the same village, but both her husband's birth and their marriage occurred within 4 miles of where she was born. It made me think that they weren't really that thorough in their search,
3) Though the details they gave of my 3x great grandmother's family appear correct, her grandfather seems to have been somewhat extraordinary in his virility. Not only did he manage to father a child at the age of 67, but did so despite having been dead almost 10 years.
Needless to say, when I first used the IGI I realized how and what this person must have done: in their desire to push backwards they just connected any two people together if they had roughly the same name and date of birth, regardless of how credible the result looked. Thus, I find it best to remain wary of those whose interest seems to be finding family ever further back. While I'm happy to look for more distant ancestors I know it's probably "healthier" to concentrate on deepening knowledge about my family's recent past (say 1800 to 1950) than providing a superficial list of names. I have a Boynton in my family, and it would only take one Google search and a lot of gullibility to get back to 1066: I only have to make a "commonsense" judgement and I'm there.