Now before I begin, I want to make it clear that I am a Canadian and therefore have different genealogical needs than most Americans. I cannot make any claims for or against the features of Ancestry.com in terms of their USA databases and information. My review here is from my own point of view.
I have hit a few brick walls over the past months, and thought that it might be time to invest a bit of dough in a pay genealogy service. Ancestry.com was offering a free 14-day trial and I figured that was my chance to see what they have to offer. I signed up for their Canadian set of databases and started digging.
At first, I was thrilled. My favourite feature is that for almost every record I found (census or vital records), I was able to view a scanned version of the original document. I have a stack about an inch high of printouts that I have yet to read through and properly organize. It was quite a thrill to find my grandfather's birth registration, and my great-grandmother's marriage certificate.
But after I gleaned what I could from my grandmother's generation, and then the generation before that, I reached an end. I didn't realize when I signed up that the Canadian records only exist for a small window of history. Ontario births are only recorded between 1869 and 1907. Ontario marriage records only between 1857 and 1922. Though the information was wonderfully thorough, there really wasn't all that much of it. At best, you'll find 3 generations of documents.
You'll notice I only gave Ontario examples there. Well, the Canadian databases at Ancestry.com would be more accurately described as Ontario databases. I think there were 2 databases from British Columbia, and a couple of Canada-wide census databases. So if your family is from anywhere outside of Ontario, there is virtually nothing here. Half of my family is French-Canadian, so without access to vital records in Quebec, I was back at my brick wall again.
Like I said, I came into this with different needs than your typical American and I suspect that Ancestry.com is a wonderful resource, for those in the USA. I think Canadians will find they run out of information after only an hour or two of searching.