"posts" what is it? articles you write, long ones. or! articles from other sites. or long things like journals, blogs or news. Think RSS (really simple syndication) automatic neews and blog delivery right here on mytribes- click the posts section and find something to read, hundreds of articles.
thats not what "personal update" is for around here, but you can use it that way too if you want! When you click "Post/Article" you get this really nice formatter that is different from the one when you click personal update. That's the big difference.
that and it gives you different buttons, and right now one of them is broken, but it is absolutely non essential, and I am about to remove it until it's fixed. (right now when you click it, it just re-directs you to the main page instead of attaching a link. it is not a serious error, and will be easy to fix when I have isolated it.)