tedster - 4:35 pm on Jan 22, 2012 (gmt 0)

Does anyone know the screen resolution of the googlebot?

Googlebot does not have a screen - it retrieves the source code from servers, which is then processed by the various algorithm components.

It seems clear from the screen resolution tool that Google now publishes that they are considering various screen resolutions in this new change. But no, they haven't said exactly how.

We lost a lot of rankings on the 19th on a site that had three adsense units above the fold.

It sure sounds like you are affected by this change, both from the timing and the characteristics of your layout. Please keep us posted bout this, shri - any changes you make as well as ranking shifts that happen.