I usually find one or two Legendary items if I happen to be playing about four or five hours... but that's not a constant, it just seems to be happening "often enough", under such conditions (I.E. playing a crap load). I unfortunately can't play as much as I used to play such games (my D2 days are long gone). I can play about six hours or so almost non-stop but only some week-ends, not all the time.
I do rarely find one "out of the blue" Legendary right after starting a game and just opening some random normal chest without any NV stack at all, in fact it happened just about two days ago in Act 2 (on MP4 I believe it was)... just started the game, went to the Oasis, killed some normal mobs, saw a chest, opened and boom, there drops a Blade of the Warlord (it sucked, but still... Legend from a chest just like that).
As for the Set items... when I see one drop and I'm playing with someone else I often joke about it and say something like "what are green items? I just saw one drop right now". But seriously Set items really are extremely rare, for me anyway, I know it's the same thing for many others, it also explains why the good rolls (not "best", just good ones) can cost you a month or two worth of constant 10 hours-a-day farming and selling. Bah... ok not that bad I guess but anyway, yeah they're rare.
I did find the IK's chest armor recently though, from a normal mob so... I won't exactly complain about set items just right now. Let's just say that they are rare but I'm one of the few out there who found something satisfying enough to just shut it down for a while. I like to still complain about sucky Lvl 62-63 Legendaries though... I laugh when I see a Lvl 63 Sky Splitter with 400 dps on it.
My Legends to Set ratio would be around 15:1 or maybe 15:2 or so.