I've learnt a great deal from the ones I've done - not only how to make a tree look good on a page, but for example, the fact that the change of year number used to happen at the end of March, meaning for example that February 1740 came later than June 1740 - wierd!
It's always a privilege to work on someone's family tree, because I have some idea of how much work it takes, and of course - it's family!
It's tricky getting commissions for family trees because those who are actively researching are, quite rightly, aware that there tree is ever changing, and they hope they're only a day away from making a big find that will give them heaps more information. And because of that, it's hard to commit to a moment to have it all preserved on paper.
That said, of course information can be added at a later date, and there are interesting ways of presenting the tree (e.g. separate giant pages in a folder) that mean that even large changes can be accommodated in the future.
So ....if you're a frequenter of ancestry.com or similar, and have found interesting information about your ancestors, why not think about having it beautifully preserved and presented?