Travisty, No, the H9's don't require any modification, they just pop right in.
Ratty, just thought I'd clarify, but an H4 bulb is a dual filament bulb (highs and lows), and used in bikes with only one headlight. The H7 and H9 are single filament bulbs.... the H4 is just as bright as the H7. So, with the ninja's wiring, the H4 will never use one of it's elements. No attack intended, just thought I'd save somebody from spending extra cash. If I'm in the wrong, let me know.
Another general clarification: Power does not equal color temp. So, you can have a 35W, 55W OR 70W, 3500K bulb. Or you could have a 35W, 55W, OR 70W, 8000K bulb. The power is how much energy the light puts out (and how bright it is), and the color temp is what COLOR the bulb is.
Thus, a 35W, 8000K bulb will not be that bright, but be blue/white and SEEM like it's brighter.
A 70W, 3500K bulb will be very bright, but orange/yellow/white and SEEM not so bright...
So Eric hit it on this topic. Different temps (colors), for different driving conditions, but you probably want to go as bright as possible.
My impressions of the stock H7's = plenty of light for my reaction time. I've gone screaming up a canyon late at night (no cops

), and been just fine, seen all the deer and have never gotten into trouble yet. But, more light is always nicer... Hope this helps!