not sure about a power cable supplied for the 660
I does have a power cable. In fact it comes with a charger and car cigarette power cable and a RAM mount too. The bike cable is different (I believe) to the 550 in that it come with leads to plug a mike and ear phones and a mini USB cable for the traffic reciever.(I believe the 550 just has plugs on the side of the cradle - which I think is perhaps a little neater)
The RAM mount on the 1200 places the 660 just where I want it - above and forward of the instruments and in easy reach - so I don't see the need to splash out another £100 or so on a TT cradle - though it would be lockable.
I have found some useful advice on wiring it up to the canbus. I got a plug from Vines for £9 (which is the cheapest thing I have ever bought from BMW).
http://www.ukgser.com/forums/showthread.php?t=117400&highlight=canbus
Finding the canbus plug on the bike was the hardest part.
I can't hear Emily at anything over 5 miles an hour , but so far I have found the screen information is more than good enough not to need a headset.
The screen is big and clear and easy to use though I have not used in very bright light yet.
Here is some good advice on unlocking Mapsource
http://www.ukgser.com/forums/showthread.php?t=186719
I found registering the device the hardest part but once I had turned the anti virus off it worked fine.
http://www.ukgser.com/forums/showthread.php?t=194337 Mapsource looks a great tool for planning etc, but I suspect if you have had previous models you know that anyway.
Downside? None really though the business pak where I work, which in 8 years old is not on the map, but is on my (car) TomTom Go
This is my first bike satnav so I can't offer any direct comparison with the 550 or the TomTom Rider but after a week's use I have no regrets yet and I think it is better than my old TomTom.