Ask most estate planning attorneys about form mills and estate planning form websites and they'll tell you that they love it. That's because for one, it gets the public thinking about their wills and trusts, and second, those who partake will eventually end up in their office anyway to correct the mistakes made during the first go-around.
I had a client in my office a few months ago who had used the WillMaker computer program to create his estate plan. (You can also find form stores around town and the ever present LegalZoom to achieve a similar result.) I examined his documents and found that despite his best efforts they had not been properly executed. In all likelihood, they would not have been accepted at probate court. He pointed out that he had formed a trust so probate was unnecessary, but of course he had not actually funded the trust, so it wasn't worth anything more than the paper it was printed on. There were a host of other issues and we eventually scrapped it all in favor of a new, professionally-prepared estate plan.
I often use the metaphor of the off-the-rack vs. expertly tailored suit to emphasize that while the material may be similar between what you can find online and what an attorney will prepare for you, the actual fit of the material is what you're paying for. Like most other professions, you are paying for the expertise and experience to guarantee a superior result.
We live in a do-it-yourself culture where just about anything you want to know, you can find online. Often that provides just enough information to make someone dangerous. While I encourage people to learn all they can about planning their estates, I also encourage them to seek a professional for the actual drafting of the necessary documents. Why go through all the trouble of forming a homemade plan on their own that could very well fail, resulting in thousands paid by their heirs in attorney's fees for probate? Much less can be spent on a competent attorney who will do it right the first time.