I have received on average at least one threat of a lawsuit per month since roughly 1998, which is when we started getting a little larger online. As a rule these threats come from the United States, and equally predictable once I outline the legal situation to them they change their tone and become polite and reasonable individuals.
I think that for bloggers the same holds, simply add an international component to your situation and the cost of 'because I can' legislation goes up so much that you might end up resolving things amicably instead of through the courts.
I also have a rule that anybody that does not want to be reasonable has to sue me, that is, they actually have to follow through on their threat. To date that hasn't happened.
So most of this is all bark and very little bite, but I'm sure that it is possible to be sued for blogging or operating any other web property, it just hasn't happened to me yet. If you go out of your way to slander or libel someone then of course you're just as culpable as you would be 'in real life', after all the web is an extension of real life.
Just like lots of other activities can get you sued. Just be a bit more careful when you criticize someone in print than you would be if you spoke out loud, that should take care of most of it. 'It is my opinion' goes a long way towards solving most of this.