I have just noticed that since Panda kicked in on 24th Feb, the Google Analytics "Connection Speed" for all visitors is all bundled under "Unknown".
In Google Analytics, under the "Visitors --> Network Properties --> Connection Speed", looking at the graphs for Cable, DSL, T1, Dialup, etc, they all show sharp drop to ZERO on exactly 25th of Feb (I am in UK, so this would be 24th in USA).
At the same time the "Unknown" category has risen on the same date. I checked this on 5 different sites and they all show the same.
I am wondering whether this is a bug (and if so, can we learn from it) or is it a piece of information Google does not want us to know any more?