I never have Bud. My FXR and wife's Softtail made it up there no problem. Didn't foul the plugs up by the time we got up there. My Victory is EFI and goes through anything. But I did rejet the HDs when I moved up here from AZ.
I've got a Mikuni carb on my bobber. I live at sea level on the Gulf Coast, but I've ridden it to Sturgis twice without issue...except for the 85 octane I've had to fill up with in No-where, NE because that's all they sell. Talk about power robbing. I rode down through Denver on the way home one year and didn't have any problem, but that's only about 5000 feet.
I'm going to jet my CB750 for riding around here and the occasional trip to the Texas Hill Country, which is only about 2000 feet. My sister lives in Durango. We're planning a trip out there this summer. I'm toying with the idea of trailering the bikes up there, but I'm wondering if I'll have some trouble at that elevation.