Although I was given some questionable break-in advice from the salesperson who delivered my bike ("Yeh...just rev the nuts off it once in while for the first coupla hundred k's....it won't hurt it"), I've stuck to the old-fashioned method that I've used for years with bikes and cars:-
I kept the RPM's under 4000 rpm for the first 150km's, and under 6000 rpm until the odometer showed 300km's.....it's SOOOOOOO tempting to buzz it higher, but there's plenty of time for that. I'm now letting it rev up to 8000 rpm, with one juvenile burst to 10,000rpm yesterday just for the heck of it.

The main thing is to strike a happy medium....
don't let the engine labour, let it spin freely all the time without over-revving, and DON'T USE FULL THROTTLE until you see at least 1000 km's on the odometer. Use the gearbox as much as possible; it's not just the engine that you're breaking in. I'm sure some younger folks here will scoff at my cautious approach, but it does work.
I've now got 600km's on my FZ6 and it's really starting to settle down...some of the annoying high-frequency buzzing is disappearing, and the shifting has changed from a loud CLANK to a manly THUNK.

The transmission howls quite a bit in 4th gear, but I'm guessing that's normal. (Actually, I'm HOPING that's normal....the last time I heard a transmission howl like that in 4th it was my old Bonneville, and the gearbox seized up at 90mph. Very exciting...)