On Greece... People in Greece recently haven't been able to get their money out of their bank accounts. ATMs in Greece have been slapped with a 60 Euro daily withdrawal limit...! (That's about $67 US dollars.) It effectively "locks" their life savings in the bank, so they can't get money out, except in a tiny dribble.
A couple years ago in Cyprus, uninsured bank accounts were "raided" by their government, which imposed a 47.5% "levy" on those bank accounts! That is, they took almost half the money of people with uninsured bank accounts...
So, this can happen. Governments can - and sometimes will - raid people's bank accounts to pay debts.
However, what I think Americans (and some others) have to worry about more is the potential to be hit by civil asset forfeiture laws. That's where the government can take your money because they think it has links to crime. They don't have to prove it in any way, and you have to go to court to get your money back (you're guilty until proven innocent). And that's if you can afford to go to court after they've already taken all your money!
Of course, many in small business need lots of cash at times - to pay employees, for instance, or to pay for equipment. That money can be seized at any time by the government, without you being charged in any way.
Here's an article about a small business owner who lost his money this way, simply because he was carrying it around when he had a minor traffic infraction...
Here are some people who had their house seized, because they sold it to a guy who the government suspected of crimes, and they agreed to an arrangement where he would pay for it later. The sellers had no connection to the guy's crimes, but the government took their property anyway. They ended up virtually bankrupt.
That's why it's a good idea to have the bulk of your assets in a form the government can't easily take from you. However, that's easier said than done!
One way could be by having assets in intellectual property. For example, I think if you own copyrights, it's perhaps more difficult for the government to "seize" them and turn them into cash (which is what they really want). It's a lot easier for governments to seize a fancy car, or a real estate property, or cash in your bank account... which is something they understand much better.