I think that the killer app for a computerized voting machine would be to allow the voters to later go back and confirm that their vote was registered properly. When I put it in the machine, I always feel like my ballot is going into a black hole.

You get this when you vote your shares for a public corporation. But, there's no anonymity. For public elections, you want voter anonymity for a lot of reasons. If you could ever tie a voter back to their vote, you could use that to intimidate them (if they vote against your preferred candidate) or bribe them (as a reward for supporting your preferred candidate). As such, once you leave the polling place, there should be absolutely no way to prove to anybody, yourself included, that your vote was tallied correctly.

On the other hand, you're rightly concerned about the "black box" effect of wondering what happens when you cast the ballot. That's why we support having paper in the system. Paper records are much less malleable than electronic records. If you saw the physical paper that was printed by your voting terminal, you'd have somewhat more assurance that your vote would be around to be recounted, among other things.