If you go to the Garmin website you will find that the full price for the Zumo 665 is $799.95. Then if you go to the Harley accessory site and look at their offering, the price is $999.95. I realize there are a lot of folks who pay way too much every day to buy stuff with the Harley logo on it, so rather than make any disparaging remarks I'll just leave it to you to decide if buying it from H-D is worth an extra $200.
BTW, you can get the Harley unit from some of the discount dealers, but none that I've checked actually discount it at 20%, and after shipping charges it's not even 10% (ie. Zanotti's $888.75 + 42.54 shipping, Surdyke $849.96 + 68.00 shipping, etc.). You can also get the Garmin at a discount from some of the electronics stores, but nothing close to the discounts available on the car models. Best price I saw online was around $765 including shipping.
I guess if the NIM (navigation interface module, $150 additional) is important to you, you will be stuck paying Harley their extra profit since I don't think the Garmin version will work with the NIM. As for the warranty, my experiences (and those of the folks from Consumer Reports) have been that if this sort of product is going to fail, they tend to do so sooner rather than later. So I don't give much weight to the supposedly longer warranty from H-D. You are basically paying $200 extra for the extra year, I think you can do better buying an add-on service contract for the Garmin from most retailers if you really think longer coverage is necessary.
For me, it all comes down to how much you care about integrating it to the radio. If I didn't care about that feature, I'd save the $200 plus the $150 for the NIM and just stick with the Zumo. As far as that goes, I'd probably save another $150 and just go with the Zumo 660 without the XM traffic and weather stuff. I've got a Garmin with traffic in momma's car, and it's been a worthless feature so far. And if I want weather updates I've got a weather band on the bike, and weather stations on the car radio. I can also stick my finger out to check for wind and rain, and use my eyes to peruse the sky for obvious signs of impending doom.
JMHO - Jerry