It's an expensive, maintenance intensive, perky sport-tourer with a shaft. BMW bikes are definitely not BMW cars in terms of performance and reliability, I speak from experience. The 'Busa is much more basic, reliable, and will be faster...
...though, let's face it, even after that shaft sucks off 20% of the K-S's hp we're still talking about a pair of really powerful motorcycles. Get to know and love your BMW Motorrad service manager, however, I'm telling you now.
Given that all motorcycles are adapted by their owners and don't stay stock for long, consider what you will want out of a fast sport-tourer. The Hayabusa, even with its vintage, is and will be readily more useful and enjoyable, bottom line.
Bear in mind, also, that BMW motorcycles represent something like 3% of all sales in the US, though that's their largest market outside of Germany. They never have had the volume necessary to achive Big Four quality control.
A side effect of this low volume is an air of exclusivity, which they play to the hilt in marketing (that annoys me). Another side effect is that BMW service has necessarily become second to none, but the dealerships are also far apart.
A 'Busa is a hard-core riding machine -- all business. A BMW is a rolling jobs program for mechanics and parts counters.