A WebmasterWorld has tons of reports from various Google AdSense publishers that (1) their ads are not loading or loading incredibly slowly for them and (2) their ad stats seem way too low relative to the norm. The thing is, normally, you would see some threads at DigitalPoint Forums also, if this was happening at a very wide scale, I could not find a recent thread on the topic (I could have missed it).
The number of unique reports are well over 10 at the WebmasterWorld thread, so something must be going on.
It appears that the slow load times are happening in the UK, but I cannot confirm this.
Forum discussion at WebmasterWorld.