I got my autosomal dna results last week. I think it's definitely a worthwhile investment although I am listed as cousin to an awful lot of people to whom I can find no link from our trees. It sounds like a lot of you have the same problem. What really bugs me is that so many people don't put a date or place on individuals in their tree. It would be helpful to at least put an approximate date of birth or a general area. There's no way anyone can find a link otherwise. Also, many of the trees are so incomplete that a link could never be found. I wonder if some people think the dna test is going to fill in their whole tree for them? My other gripe is that so many of my "cousins" have private trees. I guess there are reasons for that but it's hard to understand what the big secret is. If you're going to do a DNA test to find cousins, at least you could make your tree open to people. There's no way I'm writing to all those people to ask permission, so we will probably never find the links there.
I did find a "cousin" who linked to an ancestor of mine who I was not sure of. This was on my brick wall, so it was encouraging to know that I'm barking up the right tree (lol). The test also confirmed many other lines in my tree.
I'm going to have my mother take the test next as she and my father had some common (though not related) surnames. Some of these are brick walls on my mother's side so it will be very helpful to know which side the surname links to.
As time goes on and more people take the test, I think it will continue to be helpful. It's kind of like the "gift that keeps on giving." I wish you all luck finding links and growing your trees.