I've just bought a FZ6-SA a couple of months ago, so I've been watching the fuel usage closely. On my last tank, I got roughly 48 mpg (imperial) or 5.9 l/100 km (metric).
I always fill the tank up to the brim whilst the bike is on the centre stand, and always use super unleaded (98 RON). The bike is completely stock at the moment, so it's easy to keep track of fuel consumption, i.e. remove all the variables apart from riding style (e.g. normal / aggressive).
I was watching for when the top bar on the fuel indicator disappeared, and it was at around 62 miles (100 km). However, after the last time I filled up, the top indicator bar disappeared at 45 miles. I didn't think I was riding more aggressively than on the last tank, so I'm stumped as to why this was the case.
I'm going to run the bike for a few more tanks just to get a good average mpg before I upgrade to NGK iridium sparks and K&N air filter, as I want to see if I notice any difference in fuel consumption.
To be honest, from what I've read on this site, I'm pretty happy with the current fuel consumption. Considering I'm a big lad and I'm riding the ABS model, that's more than fair.
One thing I always do, is warm up the engine for a minute before setting off. I think this makes a bit of a difference to fuel consumption for short rides. At least, it's certainly not as jerky in 1st and 2nd gear when I take off.