I weigh 270 and on a decent hill (probably in the 3-5% range, but that's just a guess) I go around 8-11mph, and I'm 6'-2" tall.

I've been riding since August of 2003 (significantly less in winter), and I haven't lost a single pound. However, I know I've significantly improved my fitness level, and I have built some nice muscles in my legs under the fat that's still there. I'm starting to breeze over smaller hills that used to leave me huffing and puffing. It's the long climbs that can still knock me out, as I can't pace myself properly and I overdo it on the way up.

So I'm not a great hill climber, but I'm getting better. I'm not losing any weight, but I'm not gaining weight either, and I haven't (nor do I plan to) changed my diet, so it's not too bad.