I've found the coolest site on the net if you are interested in Japanese, and have to admit that I'm now a bit of a junkie. It is called Mixi. You can find on join groups on virtually any topic on Mixi. Especially great for learning kanji with the help of the rikaichan FireFox plugin (or Jbrowse for IE):

http://www.polarcloud.com/rikaichan/

Here is the community I use most, called, "Japanese<->English Language Exchange":

http://mixi.jp/view_community.pl?id=1230268

It has tons of Japanese people willing to help you out with whatever aspect of learning you are interested in. There are a lot of other great groups. Definitely recommend taking a look at Mixi.

Sounds good, but it appears to require invitation to join and all the content is members only so I can't see even what it is about

I am a member of mixi and will gladly invite anyone who wants in, just shoot me an email with your email address.

I've heard great things about it, but I must admit, I'm a bit intimidated...

its ok. i wouldnt say its the best thing ever. if you like reading blogs / peoples diaries its pretty good. you can also keep a diary yourself that people post comments on etc.

for me the best thing for studies and getting to see words used in real context is and probably always will be google.

You can find a brief tutorial on getting set up here.