The rebuffering seems to me to be a Ruko-specific. Here's why...
I just signed up and was absolutely delighted when I was able to watch the Ashes within about 3 mins of signing up for Willow.tv. So far so good. However, then I start getting rebuffering issues VERY regularly, on two levels. First, I get the rebuffering screen. But, worse, when it "recovers" it takes me back about 30 seconds in the programming. And to make it worse still, this is happening for me about every 2-3 minutes, if that. So, I see a score of something like 11/1 on TV - and 34/1 on my laptop because the TV version is getting further and further behind. Hardly live. I don't understand why rebuffering can't also get me back to live instead of just falling further behind live.
Why do I think this is specific to the Ruku implementation? Well, if I stop the TV version (can't stream from the laptop and the TV at the same time) I am always bang up to date, no rebuffering, on the laptop. And it stays that way and is very reliable. On the exact same Internet connection I get the aforementioned rebuffering on the Roku. In fact, the Roku has the advantage in that it's hard wired to my switch, whereas the laptop is wireless to that same router/switch.
To be honest, the frequency of the rebuffering and the fact that it ends up replaying the last 30 seconds (and getting further behind live) makes the experience on the Roku completely unwatchable. I'd be interested to know if there are investigations underway that might improve this situation.