Here's my feedback after playing with the demo tree that's on your front page. The demo looks very nice. It's attractive and makes me want to interact with the page. That's great.

The one time I built a family tree graphically was when my kids had a school project to do. We wanted to print a nicely organized diagram but couldn't do it with the tools we found online. We ended up printing out the information from a text file and organizing it ourselves on a sheet of paper. I don't know if I'd have paid for something or not at the time. It definitely would have been a one time use, though.

Overall I expected the interaction to be more like a modern maps interface (think Google maps) - zoomable with scroll wheel, click and drag to pan, etc.

The click to navigate seemed outdated. If I want to move up and to the right. Click the button on the right, now click the button on the top, now to the right a few more times...

Same feedback for the time line. It's a neat idea but I expected to be able to navigate by dragging it around.

Also, the zoom +- would be easier to use if they stayed in a fixed location. Having them centered based on the size of the zoom scale meant they kept jumping around. Really hard to click, click, click to zoom in.

If navigation were a little easier and more fluid I could see using something like this to create hierarchical diagrams. Right now it was too frustrating to examine larger trees.

I hope the feedback helps.