Regarding using TurboTax for eFile, yeah that's a point of trust that I don't think can be avoided. I assume that there's some requirement for Intuit to eventually purge eFile data after it's been successfully transmitted; but of course there would be no way for any of us to verify that's actually being done.
It would be nice if the federal and various state eFile APIs were publicly documented somewhere (and IMO they should be, since we the taxpayers are paying for that infrastructure). I've just never looked into this so have no idea if they are.
