I'm against complete anonymity on the Internet. While it allows people to freely express themselves without fear of being judged, it also lacks the consequences of actions other media has. As for sharing our personal information on the world wide web, I figure there are so many other participants also online that unless there was someone out there specifically targeting you, we shouldn't worry about releasing our info as long as they don't get too intimate.
From my experience, I oftentimes feel more comfortable opening up and revealing myself in the online world than in the real world. A simple example: while I sometimes have trouble reaching out and talking to someone I just met, adding them on Facebook and then commenting on their updates comes so easy and doesn’t feel awkward at all. I think it is because, like Victor said above/below, we are able to hide behind our computers and not have to risk possible humiliation, judgment, and basically, the vulnerability that face-to-face contact brings. However, this can also be unhealthy. I think we should be able to communicate fluently in person and through this type of media.
Personally, I think it's a little weird due to the fact how impersonal online communication is... it's so impersonal that it's almost impossible to be 100% sure that the person behind the computer screen is the person they claim to be (we've all heard in high school the horror stories of the girl that met some guy in an online chat room and got raped/assaulted when they met in real life.) Furthermore, by communicating personal details online, it reaches a lot more people that one intends, which could be potentially harmful.
That being said, it's a lot easier open up online and share. Also, it has long ago being a norm in our society.
I believe that you shouldn't put so much personal details out there because now a days, it's really dangerous. Anyone can access anything so it becomes unsafe when you start putting too much out there. However, it does allow people a way of finding eachother and staying connected if they are on opposite ends of the world. But then there is also that negative side again where anyone can find you and can put you in a dangerous position. Basically, going along with what everyone else has said so far, you just have to be careful with what you put out there and who you talk to, because the computer is a very good "screen" to hide behind.
If by personal details, you mean, habitual characteristics in my daily life, it's not too much of a problem. Though, if you meant social security, valuable pin numbers and etc., then that's a no go.
Semantics aside, I support anonymity on the internet, since really, it's the only actual place where you can really do what you want (excluding the child porn). Not to say I am against communicating personal details as I fully support blogs and other types of sites that flourish on self-expression (though, I particularly hate Twitter, Facebook, MySpace, and other similar sites). I should note I prefer internet discussions more so than person-to-person seminars, definitely more comfortable.
In my opinion online information sharing is not as big a deal as a lot of people make it out to be. True there are cyber predators like sex offenders and other criminals who take advantage of and abuse the availability of personal information on the internet, but that doesn't mean that all forms of interpersonal relationships on the web are dangerous. The best thing to do when joining public chat forums or other such groups that require intimate details about who you are is to be cautious at first with how much and what kind of information you release. For example, this program that we are involved in right now is asking for a lot of personal information about ourselves and is going to make our projects available for everyone to see online. This doesn't mean we have to be worried about being stalked or becoming victims of identity theft. Projects like these simply allow individuals to open up and discuss details about their lives that could otherwise be difficult or embarrassing to talk about face to face with their peers. So overall, there are obvious negatives to revealing too much information on the internet to the wrong sources but at the same time there is a world of useful resources that poses no harm to any of its users.