I've had my new R1250GSA for exactly a month now and have just over 400 miles on it (which means I've put a bit over 300 miles on it). Considering being out of town for 10 days and it being winter (and the fact that I just generally don't drive very much these days) that's not too bad. Unless the weather turns truly awful I should hit the 600 mile service sometime this month.
I'm really enjoying the motorcycle. When compared to the old 1150, it is definitely and obviously a superior machine, although I have the 1150 so well sorted and customized to my liking that I am still able to do more with it. The 1250 is faster, has much better fuel economy, is better balanced, etc. But it also has much more road oriented tires. When these tires wear out I may put something more off road oriented on, or I may not. The ergonomics are different than the 1150 for off road, and I'm finding the position references (seat, tank, etc.) differ with the 1250 when standing up riding.
There hasn't been much customizing I've done yet. The bike came with the BMW Nav mount and I got an iPhone adapter for that. I put the bike on a bit of a diet, removing the center stand and then the pannier rack mounts since I don't intend to run panniers, at least not on a day-to-day basis. I think the bike looks cleaner and it saved something around 10-12 lbs.
I've thought about deleting the passenger seat and luggage rack, and replacing them with a purpose built parcel shelf. For now, this works fine and although I haven't had a passenger on it yet, I expect I will at some point, so I'm waiting for the time being.
I asked for (and received) a discounted GRmoto muffler to throw onto the bike and review. I haven't put it on yet, since I need the time to do a good review. But the stock muffler is too quiet for my liking. There is still a level of engine noise when you get on the throttle, but this bike has a good exhaust note. The stock muffler is bulky, heavy, and unsightly as well as being too quiet. The GRmoto muffler claims a >7 lb weight savings, so getting me close to 20 lbs removed.
I did get both a heated vest and heated pant liners (Hotwired brand) and have some heated gloves coming as well (same brand) which have done a lot for helping sustained comfort in cooler riding temps as I intend to keep riding it over the winter.
No regrets. A fantastic machine.