Oh yeah, actually that would be beautiful.
Notebooks
Tags
Saved Searches
With these you could use saved searches as notebooks itself, with the upcoming hierarchical tags tags itself will be more like notebooks as well. I think that would be a really good feature, indeed.
In addition: The possibility to easily activate tags and the Notes list shows Notes associated with that tag. BUT: you could have the possibility to activate more than one tag to have the AND functionality (deactivated ones are grey).