I've had my K12GT SE since Sept 07, I've done 13000 miles on it and it's nothing short of awesome. It's perfectly capable of holding og R1's on acceleration. I've surprised a few when they saw the panniers and assumed it was a slow old tourer :) I had a ZX12R as well as this at one time and being fair there was not a lot in it to separate them performance wise.
I specified the higher screen from new and when fully extended 90 mph is relatively peaceful behind it.
The cruise control works brilliantly, only point I would make as a criticism is that the minimum the cruise can be set is 31mph. I'd like it to be settable at 30mph to make scamera dodging a little easier :)
The tyre pressure monitors work well and advise when pressures are getting a little low.
The Automatic Stability Control works well, reduces power when it detects the rear wheel spinning up, which given it's 152 hp is all too easy to do if you're cack handed. I also found when coming over rises on a favourite stretch of road at 80 mph I used to tweak the throttle on previous bikes to get a small wheely over the crests. The ASC stops such tomfoolery and reduces power to bring the front wheel back to earth gently. It's switchable if you REALLY want to wheely :)
Luggage capacity is huge, especially with the optional large top case. The BMW tank back is not to firm a fit, bit disappointed really for a factory item, but it does clip on easily enough.
Electronic Suspension Adjustment is a godsend. Set it on comfort mode while traipsing up the motorway then when you arrive in the Highlands flick a button on the move and it'll tighten up into sports mode.
Brakes are incredible, very powerful, and semi linked, I originally was unsure but now I'm used to it I like the system. Backed up by the ABS they're a formidable stopping setup!
Seat height is a tad lofty, I'm 32" inside leg and don't find it a problem. On mine they're equipped with rider and passenger seat heaters and combined with the heated grips they add incredibly to comfort on longer chilly rides.
The On Board Computer system displays ave/current fuel/speed. At motorway speeds 75 to 80 on the GPS I was getting around 55mpg which is incredible. Especially compared to its peers! Allied to the 24 litre tank it gives a fantastic range.
The DuoLever front end is simply stunning, almost zero dive from the front end under braking means at night the road stays well lit from the K's huge Xenon HID white headlight.
There's little underseat storage but I have managed to store a tubeless repair kit in the seat cowling panels. There's a little glove box in the fairing under the twistgrip.
About the only complaints I'd have is theres a clunk into 1st gear, I'd really like to have had a radio option. The R1200RT has a radio so why not the GT? There's certainly room under the left fairing panel. I looked there's a nice radio sized space there :)
Oh and for a bike that with all the toys cost over 14000 quid new a toolkit would be nice. The supplied tork spanner and reversible screwdriver are a bit pants!