Oddly because I have so much music, its not worth it to me.
I have around 60 gigs of music alone (just music, not including videos, etc). If they made an 80 gig iPhone, I'd almost definitely buy it, but to me there isn't a real difference between 16gb and 8gb, since I am already having to manage it with playlists. I usually just do a random sampling of 4 and 5 star rated songs, and there is no way I'd listen to them all before the next time I synced over night (which is when I rotate my playlists).
Sometimes I just pick artists and/or albums I want to listen to, and with that method I don't even usually fill up more than 2 or 3 gb.
While youtbue is fine for me on the iPhone, I don't particularly enjoy watching tv shows and definitely not movies on the iPhone, which could possibly move me into the 16bg camp.
If this one breaks, (I have an 8gb 2G) I'll probably just see if I can get a really really cheap 4gb, since almost nobody buys those things.