My take on immigrationwatch.com is that it's pretty useless. Most of their information is based on extrapolating out of date data as far as I can tell.
My I-140 was approved on 6/9/04 but immigrationwatch tells me that I still have a 50/50 chance of being approved by 11/12/04.
I also went through a bunch of I-140 cases a while back using my ND (10/23/04) and ND's from XX/23/XX for the 12 months before and this seemed to show that most of the data is based on extrapolation (the approval % increased constantly with each month in way that was much too "regular").
ETA