Developer hooks to process pages before they are returned to the user?

I am thinking of updating the Typogrify http://code.google.com/p/typogrify/ system for EE2.

Unlike Jens Bjerrehuss’ earlier version http://bjerrehuus.dk/blog/jens/article/improve-the-typographic-style-of-your-expression-engine-websites/ I would like to avoid introducing extra EE tags, which might confuse end users who are maintaining the site. Instead I envisage a plugin which processes the outgoing html before it is sent to the user’s browser, doing all necessary substitutions to prettify ampersands, smarten quotes etc. As a fall back I could transform the text when the user saves it to the database (though I’d rather not).

Is there a hook which lets me intercept the html en-route to the user? Alternatively is there a hook which lets me intercept channels when the user presses save (as a fall back if I do need to update the code in the database).

Is this even a good way to proceed? Please could you point me at the appropriate part of the developers manual?

EDIT: my thought is to write a plugin which lets the user enable/disable this feature and parameterise some choices (e.g. choice of font for ampersands)