cached templates...

Hello,

Could someone give a brief explanation on how the cached templates logic
will work?  I have read what the Rev. 0.37 Specs. have to say about it,
just looking for more discussion on it.  
I am wondering if it will be possible to cache sections (not sure if
this makes sense), or would this be done best by using the 
{{include some_template}}
command?  I'm thinking that if each page on a site has a navagation bar
that is generated from some db info but it only changes once a day then
will that need to be in its own template file in order to be cached?  I
assume so.

Aaron