I did a search, but didn't see a lot about the Zumo 660, so here is my experience. I bought a new Zumo 660 last year, but never got around to installing it until recently.
Installing it on the bike was the easy part, after deciding where I wanted it. I kept seeing others recommending centre high mounted above the dash. I even bought a PWD shelf with the intention of reinforcing it and mounting the GPS there, but I've been so used to having my Garmin 60Cx close to my left hand controls, I just couldn't convince myself that changing to dash mount would be good for me. I ended up using my existing bar mounted Ram ball mount and am quite happy with it there.
The wiring harness was a perfect fit for this location as well. It reached perfectly to my under seat tray mounted fuse panel, with the audio and data terminals having just enough length to lay in the tray as well. Had I mounted the Zumo up above the gauges, I doubt the harness would have reached.
Now the difficult part. I had a hard time getting it set up, it was one problem after another. First the software didn't want to load to my computer(fairly new Win7 Pro). Then I couldn't get the maps unlocked, or updated. I couldn't register, because the unit wasn't 'found' by my computer. The numbers on the registration form didn't match my unit. I never did use the long serial number for unlocking or registering my unit, so I can't quite figure that out.
After many attempts, rereading the guide, somehow I managed to get it going, but I don't know how in the end. It was very frustrating and had me really regretting this purchase. Even now, after using it for a 4 day 3000km trip, I feel that it could be so much better. I'm even thinking of running my 60Cx along beside the Zumo, and that shouldn't be.
Maybe some of the problems I am experiencing can be rectified with changes in settings, I don't know. I know I feel like this unit, that I paid close to $700.00 for by the time tax was in, should be better than it is.
Battery cover... Can't do anything with the battery cover open, even though it has to be open to connect the usb cable. When setting things up, had to open battery cover, connect cable, load maps etc, disconnect, replace cover, try unit. To make any changes, repeat. Seriously Garmin, give me the warning if you must, but let me keep the cover off while I check out the changes I've made. Seems like a small thing, but unless you've tried the fiddly cover, you won't appreciate this.
Bluetooth... Sometimes has great difficulty with Bluetooth connection to both my phone and my Scala. Once connected seems to work well, it's getting connected that is a problem. Sometimes it will announce 'phone has disconnected' even though I didn't have my phone paired.
Track log... The track log seems to be very limited. I got home from 3000km 4 day trip, and wanted to check back at my route, and it only saved some of the last 2 days. Maybe 1200km of the trip. Can this be changed? On the old 60Cx, could save track log daily. Can I do this on the Zumo?
edit... Looks like I can save a track log to 'archive' but I still can't see any information on how much the unit will save without doing this.
MP3 player... MP3 is pretty basic. I had a $39.00 MP3 player that does a better job in managing my MP3 files.
Traffic receiver... Traffic data can only be received with optional traffic receiver. The traffic receiver is a power cord that plugs into a cigarette lighter. This is supposed to be a unit designed for motorcycles. My $100.00 Garmin 265t I use in my truck came with the traffic receiver cord, but not with the $650.00 Zumo??? Seriously Garmin?
Also, every time you make a selection on the touch screen, it sends an audio signal to my Scala cutting out the fm radio of the Scala. So even if you just want to check the direction, or coordinates, the unit sends out a priority audio signal. Maybe I can re-prioritize?
Little thing, but I miss the little north arrow from the 60Cx. Yes, I could select direction for the data field to be shown, but I already use the changeable data fields for other info. Garmin, just put the little arrow back on the map page.
Even with the latest map updates, in the week that I've been using it, I've found many areas that are not up to date.
One last little thing Garmin. Could you put a hand strap hole and include a hand strap? I've always used the hand strap on other units as a back up security tether. I just loop it around my mirror. If the unit becomes dislodged, it won't go sliding down the highway. I had to mount a little plastic ziplock anchor and use an old camera strap. Even for hand use, a strap would be nice.
I'm still not overly impressed with it for the price, but it's not all bad. I do like the larger screen. It seems bright enough in all but extreme bright conditions. The speed warning for certain highways works well, although the red colour is difficult to see. The touch screen works well even with gloves on. I like the built in MP3 even though it could be better. I like the Bluetooth audio to my Scala for navigation instructions.
It is pretty amazing what they can stick into a small package like this, but with all the other electronics out there like smart phones and tablets, it's evident that Garmin seems to be way behind in the development end.