Hi Ben,
I guess you're going to be the first one to hit the ground with Twinfield, because the accounting export of Project/Open will probably still take several months.
I'm particularly interested in how you think to resolve the mapping between the OpenACS cost/time categories and the cost accounts in the software. Also, the counter-accounts (?, sorry, I had my accounting classes in Spanish, I don't have the precise English/American terminology...) will need to be configurable, because some companies are going to account working time as maintenance type of costs, while others will treat them as an investment...
But maybe it's not worth to try to keep the configuration flexible, and a single successful case of such an interface would already have an important value...
Bests,
Frank