Ace Stream works really well for watching live broadcasts.
On demand video would be more difficult though since not everyone is watching the same content at the same time.
I'm not sure. I believe it's pretty good but I've only ever used it to watch Formula 1 streams (since F1TV most likely won't be available in my country until next year).
Unless you compare the latency to a live broadcast, you'll never know how bad the latency is.
Most P2P systems are terrible, which makes them pretty useless since you can hear who scored from your neighbor seconds or even minutes before you see it.