How many times.... OTHER TREES ARE NOT SOURCES. Other trees can lead you to sources. Nothing wrong with looking at trees to see if they've got some information you haven't - as long as you follow it up properly. Oh well, I'm sure you guys here don't need telling. 
That is the big problem, they are HINTS, not facts and not sources. If someone gives you a hint, it is meant to lead to looking for something, unfortunately people dont do that, they just copy. Even on here we still get people who maintain a date/ name etc is right as " trees I've seen on line all say that." As Ruskie so rightly pointed out, it only takes one person to record a fact incorrectly and soon it is accepted by half a dozen others as being correct.
This subject comes up regularly on here, but I'm afraid it is something that will never stop as long as certain sites advertise with such phrases as, " Just type in your name and trace your family back to the year dot! " It isn't that easy, as we know. In the end though, it is up to the individual, if they are happy to accept inaccuracies that is up to them. You'll probably find that a lot of those are people who took up offers, did their tree during that time after being inspired by a programme such as WDYTYA, and haven't looked at it since. Genealogy, as we know, is an expensive and time consuming hobby and a lot of people don't want to spend time or money on it, they want it handed to them on a plate.
