I'm trying to do some datamining on the files.  Here are some interesting initial observations:

- There are 88267 accounts with BTC balances; I was under the impression there should be more than that.
- There appear to be wallet ids in the transaction history that aren't in the mtgox_balances file.  This would explain the above.
- Some accounts have negative BTC balances (-85 BTC!).  Oops!

Edit: it looks like 0 balance accounts aren't in mtgox_balances, so you can't xref user ids with wallet ids for those.

Edit2: There are 39905 accounts with only fiat balances, for a total of 128172 unique user accounts in the mtgox_balances file.  The btc_xfer_report has 147079 unique wallet ids that have either deposited or withdrawn bitcoin.  That implies at least 18907 users who have shown BTC deposit/withdrawal activity got all their funds out.  I haven't yet gone through the trade history logs, so this is just a lower bound.