I've heard all the debate about Ancestry.com trees: they make it too easy to copy bad information, people will add whatever they want, etc. Only rarely do I hear the good comment - that they offer great hints.
I've been doing some research in a new region lately and had hit a brick wall. I always check Ancestry just in case. I figure that it never hurts... Well, surprise, surprise, a public tree referenced a publication on a family that sounds like it will be a huge help. Since I don't research in this region, I never would have checked that journal. What fantastic luck!
The longer I research, the more open I become to open-ended searches. I've found graves in other countries than expected - and this time, a set of vital records that wasn't supposed to exist.