For those who read my blog and don't know - Halvar Flake is one of THE most respected security researchers / reverse engineers in the world (he wrote a little application you may have heard of called BinDiff! ).  
He has pretty much a standing invitation to come to Blackhat and deliver training / briefings each year and has done so for as long as I can remember.  Heck he's even been to Bluehat! 

Well it seems that this year DHS put a stop to him travelling over here for short tactical training related visits: http://addxorrol.blogspot.com/2007/07/ive-been-denied-entry-to-us-essentially.html
Yikes.  And I thought not getting my luggage for 3 days in Spain was bad . . . at least I was let into the country. 

Wow.