SHOESTRING GENEALOGY: Genealogy Mistakes:
"Mistakes about national origin can confuse a family's history.
Your great grandmother may have denied a particular nationality because it was not 'the thing to be' in her day. Consequently, your grandmother might pass on to you what she believes to be the truth; in reality, though, great grandmother 'withheld evidence.'
One of the major drawbacks of family genealogies and histories, especially those published in the Nineteenth Century, is the lack of adequate documentation. As often as not, the author — in his zeal to trace the family back to the Mayflower or other illustrious beginnings — made serious mistakes. The most common one was assuming that an ancestor was the son of a particular man with the same name without proper documentation.
While vital records are the most important records for genealogists, their availability varies widely from area to area, as previously mentioned. An additional problem is that information found in them is not always accurate. Early records may not be complete, the person providing the information may have given inaccurate data either intentionally or by mistake, or other errors have occured in copying or indexing.
In using a census index, be certain that you have looked for your surname in all of its possible spelling variations. Remember also that indices, including those produced by a computer, are subject to human error. Every genealogist has a horror story about printed census indices; studies show that the error rate is high because of improper key punching or misreading of the original records. So if you don't find your ancestor in an index it doesn't necessarily mean that he cannot be found in the census. You may often have to search every name in a given county before you find him.
Gravestones, too, are sometimes erected many years after a person dies and may contain erroneous dates. Mayhap the stonecutter erred or was given the wrong information. Be careful, too, of printed compilations of cemetery records (this applies to other published material, such as marriage records), because errors can be made in copying, indexing or publishing."
Kimberly Powell, no relation, lists Top Ten Genealogy Mistakes to Avoid, in an article found at: About.com
Mistake #1: Don't Misspell the Word Genealogy . . . .