I recently tried a free 14-day trial with the OneWorldTree feature on Ancestry.com. I have an annual subscription already to the US census records, the US immigration collection, the US records, and the family and local histories. I've been very pleased with all the information I've found on this website in the past year, and thought it would be nice to try one of their other features.
I discovered that the OneWorldTree feature is excellent for those people who are just starting out on their family history research. You can type in a few of your ancestors' names and hopefully hook in to someone else's tree and add all their names to your file. OneWorldTree is definitely something you can use at the beginning of your research.
The problem I discovered for myself is that in the past year, I've already discovered many of the names through the world tree feature I already have access to with my subscription. I've already typed in manually most of the people OneWorldTree found for me. Which leads me to another drawback. OneWorldTree does not have the ability to input a Gedcom file from my PAF program. I thought I would be able to upload my gedcom file of 8500 names and that I could then search for those names. But I had to input a few names one by one for OneWorldTree to search for them.
So if you're just getting started with your family history research, then OneWorldTree is a good option for you and worth the annual fee of $49.95 for new customers (If you already have an Ancestry.com subscription it would be $39.95). I wish I had used it when I started my research a year ago. It would have saved me a lot of time and typing.