I think we just got 100% assurance this issue will get investigated. According to Al G over at The Field, not only is Obama on the Senate Foreign Relations committe with oversight on the State Dept. (ETA: And thus, the passport dust-up), so is our old pal Joe "Bidin' my Time..." Biden, as chair.
Bonus round -- the ranking GOP member is another person who's worked with Obama, Dick Lugar. Indeed, Lugar worked closely with the new Senator Obama to co-sponsored his first substantive legislation in the Senate, which dealt with Nuclear Nonproliferation.
No idea how Lugar feels about Obama now, but I think all this points to a strong sign that investigations will be done, and done right.
And I think we'll see that it pays, sometimes, to not throw people under the bus. Never know when you'll need their help...