Pownce membership is by invitation only right now, during its testing period, but I have yet to come across any gliches or problems with it.
What is Pownce?Imagine a combination of Twitter/Jaiku with a desktop* based messaging/link/file/event/photo sharing system and you will get a general picture.
Yet another social networking tool maybe. but the extra features do make it useful. Messages can be sent to individual contacts, your whole list of contacts, a group of contacts or all the pownce members. Grouping allows you to seperate your list into categories, for example, family members, friends, work colleagues, blogging contacts. The contacts you can add are existing friends and contacts plus their friends/contacts. It has a pyramid rather than the flat sort of structure that allows you to browse members and add anyone. For now at least -I do not know what plans there are for further features.
I have already used it more than I have Jaiku or Twitter, finding it more personal and immediate. I have also found a couple of my favorite bloggers on there who I have not had one- to-one contact with before.
* You do not have to download a program as Pownce can be used directly from the website rather than from the desktop interface. I find it more convenient to use via the latter method; rather than having to navigate to the Pownce site to send and receive messages.