The Odyssey PC-680 battery in my 2000 BMW R1100RT was installed on July 19, 2004 just before I bought the bike. In less than a month it will be 6 years old. For the last year it has usually been on a Battery Tender when it was not being ridden but for the first 5 years of it's life I didn't even own a Battery Tender. It has failed to start the BMW only once after having sat unridden for probably 4 months in the winter time. It turned the engine over, but very slowly, so I put the 10 amp charger on it for about 30 minutes, started the bike, and it's been fine since.
I know I've said it before, but I am so impreseed with Odyssey motorcycle batteries that I'm gonna say it again. They are, without a doubt, the best motorcycle batteries I've ever used. The one in my Spyder RT cost about $125.00. That's maybe 50% more than most other brands but well worth the deifference in my opinion. And, no, I don't sell Odyssey's or have any other financial interest in them.
As far as other brands of batteries I've used, I agree with what others have said, they tend to last about 2 years without the use of a Battery Tender or other trickle charger to prolong their life.
Cotton