uses of portlets

Hello.

I'm considering using portlets but am a bit confused, initially, about
their scope.  From my initial reading, it seems that they might be
used for rather trivial things.  I refer to the simple rendering and
action modes.

Perhaps I've got the wrong impression, but I thought I'd put this out
here to see what you think.  Can I use portlets to bring a full
fledged, complex web applicaiton into a portlet on my portal site? 
I'm thinking of making a portlet that contains Blojsom, a full
featured blog application that is implemented as a java web
application.  Is this an appropriate use for portlets?

Chad