That there are problems does not surprise me. There are problems with all of the Censuses - transcriptions, missing data, etc. I use ancestry as an addition to my research. Perhaps this is because my training as a historical researcher came in the late 1960's and early 1970's. I prefer to see the raw data as much as possible so I will take the time to go to the friendly micro-fiche or microfilm machines and look for myself. Luckily my local Library has a complete set of indexes and microfilms of the Censuses.
Newspapers are also an excellent source for the researcher. Not only can you check the data from Ancestry but you can also get a feel for the times.
One problem that I have seen is that many people seem to be lazy. Ancestry to them is the easy way to put together a family tree with no fuss no muss. But for me this is history and there is more to it then that an individual is born in 1800 and died in 1900 with 18 children.
Good points William! It is always wise to check the original of any record you find in your searches. I think the problem for many people is not so much laziness but rather a lack of understanding about the record/data source.
Many genealogists are just starting out and they don't realize that errors occur in any transcribed or indexed set of records. They also often don't realize that parts might be missing, so they don't find their ancestor and assume he/she is not there. But in fact they very well could be, it is just that either the original records aren't complete or the data provider missed whole sections when transcribing or scanning.
Some people do fall into the trap of not wanting to leave their computer chair, but that may be an offshoot of having so much brought to us now online.