When recording the lives of your ancestors, it is essential to have at least two online family trees. I always knew it was a great idea for everyone else, but for many years I resisted doing this myself. I had traveled to numerous courthouses, spent countless hours in libraries, etc., and I was not about to let anyone else steal MY research. I also knew that there might be errors, and I didn't want anyone copying my errors from tree to tree.
Several years ago I decided to try posting a private tree to Ancestry.com containing just a small portion of my ancestry. It was so easy to search census and many other records, because Ancestry did it for me through their "shaky leaf" hint system. The tree was easy to use, and I could access it from anywhere that I had an Internet connection. But then I decided to see what happened when I made my tree public. All I can say is WOW! Yes, people copied my information from tree to tree, but they also found additional information that I copied. Occasionally someone would catch an error. When I corrected the error, I noticed that the other trees would, one-by-one, get changed to contain the new correction. The best part came one day when a researcher had noticed a family Bible for sale on eBay. She searched Ancestry.com public trees for the ancestor's name and found my tree. She notified me that the Bible of one of my ancestors was for sale. I won the auction and am now the proud owner of a Bible published in the 1700s. I never again wanted any private trees.
If you are going to have any DNA testing (and I hope to encourage you to do so), online trees are essential. I find almost all of my DNA cousins through Ancestry.com, and my greatest discoveries have been made by comparing Ancestry public member trees. Almost everyone who is serious about their DNA research has a tree there.
There is no such thing as too many family trees. Post your ancestry on as many sites as you wish,but these two sites that are critical: Ancestry.com and FamilySearch.org. Here are why these two are important.
Ancestry.com is the best known website for family historians and genealogists. Ancestry has a massive subscription base, and most subscribers have their own family trees there. Once you start a family tree, you can search Ancestry's databases for records and attach the records to your ancestor's profile. Ancestry even searches the most popular 20% of their databases and reports "hints" on your ancestor's profiles. Note that they do not search all of their databases, so you will want to do your own searching. You can add photos, documents, and stories of your own to the tree. And best of all, you can search other public member trees where you will find relatives who have these items about your ancestors. I can't tell you how many great photos and other items I have received from distant cousins whom I never knew existed. All living people appear on Ancestry's trees as "Private", so their names and other information are not searchable.
FamilySearch.org is a well established website, but its newest tree system, FamilySearch Family Tree, has only been around for about a year. Instead of each person having his own tree at FamilySearch, everyone works on a common family tree. That means that we are not duplicating efforts. When you find a 1850 census record and attach it to the correct family, it never has to be found again. Everyone will see the new record on the tree. The same applies when someone adds a photo or story to an ancestor's profile. If someone adds a photo of one of your ancestors, you will not have to find it. It will appear in your tree.
Please note that you cannot search for, or find, any living person at FamilySearch Family Tree. Even if you give me your full name, date of birth, and ID number in the system, I still can't find you. Even my own children can't find me on FamilySearch, so I can still tell them I'm 29 years old! All deceased people should appear in the tree only once, but because living people are not searchable, they may be entered into the tree multiple times. Each person adds all living family members to their portion of the tree so that they can view them. Once you've added your living family (who are visible only to you), you can search for the deceased family members and connect them to your tree. FamilySearch's collection of digitized and indexed records is available directly from FamilySearch Family Tree, so you can connect them to your ancestor's profile. In addition, you can add your own photos, documents, and stories.
If you do not have a family tree at one or both of these sites, I cannot encourage you strongly enough to do so. Each system have different records and different technology. You will leave a lasting family legacy by using both systems. You can create a tree for free at Ancestry.com, but searching their records requires a subscription. Everything at FamilySearch is free, just create an account and get started.