Some researchers are using the Internet as their only tool for genealogy. I've had people tell me they don't want to bother with original records or use books. I'm afraid people that solely depend on what they find online will be putting together flawed, incorrect family trees. First, you need to evaluate the data carefully. Experienced genealogists all have stories of records that were incorrectly interpreted and then passed on to hundreds of others, causing all kinds of problems.
Scanned records can also contain errors.
When information is based on the research of others, its accuracy depends on what kind of researcher did the work. Information shared over the Internet is no more or less reliable than material sent to you though snail mail. Information can now be shared so quickly by so many diverse people that the researcher must be careful to evaluate everything shared. The Internet offers us exciting opportunities to connect with cousins and share our records. But we still have to be thoughtful genealogists and turn to our library collections and courthouses to verify what we find in cyberspace.