I used OTS for my taxes a few years ago---it worked great. Then I wrote a couple pairs of small java applets that used the data to form fill the .pdf tax forms...back then this wasn't part of OTS. I did contribute the scripts back. I stopped using it 'cause I got free tax prep from my employer after that.
OTS was great! You know what was great about it? You could understand and see every step it did. You could see the correlation between the data entered and the output all through the process.