One of the most important features of Family Tree is bringing the primarily unsourced New.FamilySearch.org information onto the mainstream as a source-centric database. Almost every entry in the Family Tree program allows the user to add qualifications, sources and support for conclusions. Users who fret over the ability others have to "change their data" miss the point of the program and are likely totally out of touch with genealogy.
In each case, uniformly, entries into a database, especially one online and available to the public, should be qualified with a source justifying the conclusion. That means each and every name, date and location needs a source. Family Tree comes very close to allowing that to happen in a orderly fashion. The method of adding sources in not unique, but it is elegant and as easy as the task can be made.
There were some rumors circulating early on, that the number of sources would be limited to 1000. This may seem like a large number, but for some researchers this would seem to be severe limitation. In fact, the Manual for Family Tree clarifies the numbers and the issue goes away. The Family Tree Manual for 5 August, 2012 at page 81, says:
Each person, couple relationship, and parent-child relationship can have up to 1,000This clarification shows that few individuals or families will ever approach the limit of 1,000 sources. Also initially misunderstood is the function of the Family Tree Source Box. It turns out that the Source Box is a "temporary" location for storing sources, but can contain up to 10,000 sources organized into up to 50 user defined folders. Any source citation can be added to a user's Source Box for further attachment to an individual, a relationship, or a fact. Once the source has been added to all of the pertinent places, it can be deleted from the source box. So, in effect, the number of sources in a user's family tree is essentially unlimited since once a source is deleted from the Source Box, it continues to be attached to the individual, the relationship or fact.
I am not so naive to believe that the genealogical community will suddenly start attaching sources to all the events in their individual data, but the potential to add sources in a non-threatening way, at least opens the possibility that more sources will be used in the future. In addition, the potential for disputes will be greatly reduced as users see that adding data to the Family Tree "requires" either justification and/or a source.
For details on how sources work in Family Tree see the Users Manual available as a PDF file in the FamilySearch.org Help Center.
One issue that looms on the horizon is that of "proper" citation form. There is nothing in the Family Tree magazine preventing those obsessed with proper citation form from inserting the mandatory punctuation and spacing, but it is important to understand that an emphasis on "acceptable" or "proper" citation form will likely discourage most genealogists from adding sources at all.
If you find an improper citation form cited for your own ancestors, please feel free to "correct" the errant source citation, but don't berate those who added the citations in the first place or you will likely discourage further contributions.