UPDATE 5:08 PM CST: I changed the time on this post to keep it at the top of the blog. There is a new mashup below, though.
After reviewing our records, we've determined that your AdSense account poses a risk of generating invalid activity. Because we have a responsibility to protect our AdWords advertisers from inflated costs due to invalid activity, we've found it necessary to disable your AdSense account. Your outstanding balance and Google's share of the revenue will both be fully refunded back to the affected advertisers.
Please understand that we need to take such steps to maintain the effectiveness of Google's advertising system, particularly the advertiser-publisher relationship. We understand the inconvenience that this may cause you, and we thank you in advance for your understanding and cooperation.
If you have any questions or concerns about the actions we've taken, how you can appeal this decision, or invalid activity in general, you can find more information by visiting http://www.google.com/adsense/support/bin/answer.py?answer=57153.
The Google AdSense Team
Yes, this is all the communication I've gotten on the matter: I have no idea what invalid activity they think my account might be at risk of generating, or why they think it might be at risk of generating any invalid activity at all. They don't, apparently, have to tell you.
Yes, I am unhappy and inconvenienced.
Yes, I have submitted an appeal.
No, I am not particularly understanding or cooperative.