It makes me think: what do I like about Gmail? * the interface (discussions especially) * the speed * the search features (and its speed) I suppose most of

It makes me think: what do I like about Gmail? * the interface (discussions especially) * the speed * the search features (and its speed) I suppose most of it could be recreated on top of a "regular" mail server but what would be involved? I'm not saying that would be easy but, wouldn't that be an interesting offering? (open-source or not actually)