Got some great mileage the other day (best I ever had on the bike) and just started wondering. I figure, answers will differ depending on the exact setup and whether you're rocking a 75 or a 100, but they all have the same tank size at least.
On my K75C, I managed 335 kms (about 208 m) before hitting the reserve light. Estimate she would have done just about 365 kms (about 227m) to bone dry. At 16 litres before reserve, that would be 20.9 kpg/59.1 mpg.
I wasn't really trying that hard, so I'm sure that doesn't even come close to what someone on here has managed with with proper riding technique, tuning, and all the rest.