So, now that people are seeing this format it will be interesting to see what happens to productivity for people. Here are some things I'm noticing regarding formatting.
728x90 Leaderboards are now starting to show actual images in the left portion of the ad space (which I think is kind of cool). Not all have them have images (essentially thumbnails) but the ads that do, have some real impact. I've always thought a text ad should be a text ad but this I find actually cool. It's almost like G responded to Media.net's layouts in the design of their new ad formats. Competition drives innovation again. Haven't seen this with other ad sizes but they're not common yet so could just have missed them to this point.
Titles are not linked in the units I'm using and don't seem sizeable. This makes them look like page headings sometimes (particularly with leaderboards) and they don't necessarily appear clickable. Flip-side of that is the new arrow which does imply clickability.
There is a slight color shift on units with panels, e.g. when you set the background color of the unit to a specific color, the panels are actually rendered slightly off of that color to highlight the panels. It's intuitive but at the same time makes borderless ads look a bit lost in space. Anyway, those are a few observations. I'm sure there are more quirks to be noticed.