Ehm... Most of the go, a good chunk of the stop, and I don't know, maybe half of the cornering day to day.
But it depends what you mean... I can use pretty much all the power the SV has to offer in a straight/fairly straight line, but in the real twisties I can't since I'm not great at reading the road or choosing lines, and that slows me down. On the track I use most of it I think... But again my cornering lets me down, and I come off the power early and stay off for too long. So the question needs clarifying I think

I'll take most of you on the drag strip but I'll be the last to get home afterwards
I think most riders would be surprised by the corners the SV will take in fairly stock trim (decent tyres maybe). There's been a couple of times on the track when I've thought "Right, I'm well over here" and then started to run wide, funnily enough the bike always has more to give. I went through Duffus something like 20mph faster than I thought I could simply by missing a braking point and having to get on with it, and the bike still wasn't pushed too far.
On the road I've got no intention of using even 3/4 of what the bike has to offer, to be honest 9except for power sometimes, and brakes in an emergency), in fact I've arrived at the level of use I'm at simply because I don't think it makes much sense to push it any harder. If that makes any sense... I'm getting better but I'm not using any more of the bike, I'm just using it more safely.