The IDF, in at least a partial shift, is now asking Gaza Palestinians to come forward with complaints regarding Cast Lead, so they can launch investigations into any misconduct. So far, IDF Chief of Staff Gabi Ashkenazi said, the military has fielded 60 testimonies and is investigating 45 claims.
My understanding is that Palestinians have historically been reluctant to come forward in these sorts of investigations for two related reasons. First, they're doubtful of whether they will get a fair hearing through the Israeli government (particularly, the Israeli military). And second, they don't want to be seen as legitimizing their enemy by participating in its legal system.
Both legitimate concerns. Also, both very familiar ones. They are, more or less, the same reasons Israel refrained from participating in the Goldstone inquiry -- belief that the commission was irredeemably biased, and not wanting to ratify a body (the UNHRC) which they feel is committed to oppressing them. It was a decision that, to say the least, did not turn out well for Israel.
Even the participation in a losing effort is often better than not trying at all. This isn't 4th grade motivational speaking -- the act of putting arguments and claims on the record can have important effects later on in history, because they can serve as the basis for continuing moral claims and reassessments that otherwise might be lost. If one fears an IDF whitewash, well, not participating in the forum won't make it any less of one, but it will provide the basis for protesting it.