Via Marty Lederman, the CIA has declassified the letter (pdf) Jane Harman said she wrote to the agency in 2003 upon being informed of the "enhanced interrogation techniques" the agency was using. (CIA's response here, also pdf.) Essentially, Harman asked the CIA, "Are you sure we should be doing this?", and the CIA responded, "Hey, John Yoo and Jay Bybee say it's OK!", and that was the end of it. It doesn't reflect particularly well on Harman, though at least she (a) expressed some concern, and (b) explicitly urged the administration not to destroy the Abu Zubaydah interrogation tape.
As Lederman writes, this is "proof positive that the oversight system is hopelessly compromised." But the operative word here is hopelessly--it's difficult to think of any workable reform that would enable members of Congress to receive classified briefings while retaining the ability to make a public stink out of any practices to which they object. Do we really want to enact a system in which a single member of Congress can, at his or her discretion, effectively thwart executive-branch decisions on intelligence activities? That's putting a remarkable degree of faith in Congress. There's a sort of parallel, I think, to the broader torture debate: it would be unwise to legally institutionalize torture just because it might be effective in very exceptional cases--and it would be similarly unwise to give the ranking minority member of the House Intelligence Committee an outsized role in making interrogation policy just because in this instance it would have produced a desirable result. Perhaps there might be some system by which committee members could formally lodge protests or initiate secret reviews of objectionable policies, but anything beyond that would seem to be ill-advised.