So everyone... My girlfriend came to visit me, and I finally got to put everyone's great advice into practice. Our riding went really, really well and we even tackled Australia's Great Ocean Road, which is an absolute must if any rider ever visits the South of Australia... I was really surprised how natural it felt having another person on the back of the bike, but I can imagine that a "bad" passenger could make for an awful ride. I could feel it when she wasn't paying full attention and was watching something instead of leaning with me... As soon as her head moved, I could feel the bike respond...
As for braking, I definitely found that with a passenger braking distance was greatly increased, but that's pretty much to be expected. And as suggested to me, use lots of back brake, it's much more effective with a passenger. I also found that the worst part of braking was any time I had to brake going down hill... Put extra pressure on my wrists and made for some sore arms by then end...
All in all, I found that riding with a passenger wasn't as hard as I originally expected, but I would definitely recommend to anyone taking a passenger for the first time, to do a short ride on some back roads, and get the feel of the bike with the extra weight. Oh, and I was really surprised at how stable I felt at any stop, I thought any movement was going to make the bike rock like crazy, but the bike was actually pretty stable at the lights.
Thanks again everyone for all your suggestions, and comments, me and my girlfriend thank you all!
Cheers,
Tom