using built-in db

I'm finding the built-in DB quite cool. Is there a reason I shouldn't be 
using it? Does anyone know what its performance limitations and points 
to consider are? The site I'm building now will probably never have more 
than 1000 total objects, and I'm assuming that should be more than fine, 
but future planned projects will have more. At what point do I need to 
give up the built-in object db?