Well I'm home after a 7,963 mile, 22 state (road test).
I encountered no serious problems with the LT. I ran 91 Octane when available but on several occasions has to settle for 89 and when available tried 92/93. My overall average fuel mileage for the trip was 47 MPG. However it did drop to the low 40's while riding in the the Rockies for 10 days. On the open road I could get around 50 if I stayed under 65 but over 65 it dropped to around 47. I found no serious performance problem associated with altitude. At 14,214 ft on Mt Evans it ran perfect which was a lot better then the operators performance!
One problem/issue did come up around 6,200 miles.
I got the dreaded 40 to 45 MPH head-shake. The rear tire was starting to show some serious wear which probably had to do with the up hill, down hill, tight turns, long sweeper turns, the constant leaning and sometimes heavy acceleration. (P.S. I removed my Surburban Machinery the first day out cause the foot pegs seem to scrape a lot on Colorado roads) I had the tires replace at Grand Junction BMW/Honda. A great bunch of guys. I called ahead and they set me up an appointment and when I got there the afternoon before my appointment they took me in and did the front and rear tires with new Metzeler ME880's. I followed Metzeler recommendation of putting 100 or so miles on the tires at under 55 mph. What I found after about 10 miles of riding the LT felt like it was turning into a HD with a lot of vibration. I took it back to the dealer and their tire guy took it for a road test and announced the the front tire was seriously "out of round". The did a quick replacement and a rebalance. The new tire required 2 and one half, 1/4 oz weights on either side of the valve stem or 1 and 1/4 oz to balance the tire. This solved the vibration but they could not get rid of the 40 to 45 head shake. It's still there after putting 5,000 plus miles on the tires. It's ok as long as you have your hand(s) on the bars but you can feel it want to start. But since I had read so much about it here I have been "checking" to see if my was doing it since I bought the bike lol.
The NAV III worked perfectly, the Bill Russell seat was great and the BMW cup holder never failed. I did start to get an annoying "squeal" on the CB when you hit the push to talk button but called J&M and they said "Yep It happens!". Had me take the headset cord apart and clean and blow out the connectors. They said they tends to collect moisture and that solved that problem.
I did get to link up with pieceofficer in Colorado Springs. Thanks for lunch.
My overall take is the BMW K1200 LT is a serious mile eater with almost all the comforts of home!