Yesterday Wizards announced (here, subscription required) they are going to slightly alter the way monster stat blocks are displayed starting with products released in May 2010. When Monster Manual 3 is released in June its monsters will be displayed using this new stat block format. An example is of the new stat block format is given, but honestly, without a side-by-side comparison it's kind of hard to tell what is really different between the current and the new version.
So somebody did just that. weebeegamers,com cut and pasted a current monster stat block right next to a new one (here) so the two can be viewed in a side-by-side format (click on the small stat block picture to view a more readable version). I think the new version is a real improvement, saying that as someone who is currently stumbling through DM'ing with monsters in a format that is new to all of us.
The initial article did not specifically say when the 2500+ monster stat blocks in the Adventure Tool would be updated, but it does say they would go into "wide-use" with the release of MM3 in June. I am guessing that when MM3 is sourced into the update for the Adventure Tools in July the news stat block displays will all be there. They aren't really changing any data as such, although it looks like they might take this as an opportunity to tweak some of the verbiage for the sake of clarity.