Well in case of the current situation there is a considerable amount of it.
People fear that the DHS seizing the mtgox dwolla account wasn't the last of it.
Satoshi dice has blocked the US out of uncertainty.
There is considerable doubt that the mtgox/coinlab deal gonna work out.
That is a fact, look around the related threads. And it is different that somebody coming along writing something like: "Bitcoin is unsafe because everybody can steal the coins, operating systems are unsafe and so is Bitcoin.". The former are concrete events with their respectable outcome. The latter is the infamous "spreading of FUD."
There are two kinds of FUD, the one based on agenda/misinterpretation and the other one based on factual events.
US Govt doesn't take something down piecemeal. Review Kim Dotcom and poker to see how they work. Just taking the Dwolla account lets MtGox change domains (off .com), move servers, move money (their accounts in Japan likely have much much much more money). DHS/DOJ don't play nice and give people "warning shots". MtGox being incompetent isn't news. They shouldn't have let people use Dwolla. The reason they were probably interested in the Coinlab deal was because they knew they weren't legal. Coinlab probably knew his and probably reported them. Again, MtGox being incompetent isn't news. It would be news if they weren't.
Blocking US ips was a smart move by SatoshiDice. It's not worth the legal risk. Americans can still gamble, they can find out how, the website was garbage anyway.
MtGox/Coinlab lawsuit will likely drag on for years, has very little to do with the market and/or Bitcoin.
CampBX uses Dwolla. They're based in the USA. DHS could shut down their entire operation. But they're still up, they're still letting people use Dwolla to get Bitcoins. So clearly it's not an attack on Bitcoins. It's merely MtGox getting caught doing something they shouldnt.
Med/Long term it was good news. People leaving MtGox, moving to other exchanges. We need more bad news for MtGox, so more people will move.