I totally agree with the suggestion for allowing uncertain entries to be added and then highlighted in some way (they could look different on a tree diagram for example). I am a stickler for ensuring I have enough sources/evidence to be sure an entry is correct (too many trees are full of dubious entries for my liking).
For now I have to create separate trees in which to store entries that I have not been able to substantiate to my satisfaction. Once I am happy I then have to merge the trees somehow. If I could create these entries directly into my main tree but be able to see easily which have yet to be fully ratified then that would be a great benefit to me.
At present it is very difficult to tell the quality of the data in other people's trees (a lot of people seem to have no sources at all!) and if they could identify themselves those entries they were uncertain about it would give me more confidence in other people's trees (well a bit anyway!).
Finally support for multi monitors would be fantastic. I have a three monitor setup and if I could have different views across multiple screens it would help a lot. I appreciate this is likely to be of benefit to only a minority of users but multi monitor setups are on the increase. When you are dealing with a lot of data (surname index, family tree views, source/media views, to do lists, charts, etc.) being able to spread the windows across a number of screens really does help.