Technically it's more like second time squared, as I'm leveling two characters to 80 right now, but the point still stands that I think now that the initial rush for most folks to get their mains to 80 is over, questing in Northrend is just plain easier.
Obviously this is in large part due to the fact that you're not competing with everyone for the same kills. When I did the Ned, Lord of Rhinos quest the first time it was a chaotic melee as something like twelve groups (groups, as in two or three people per) vied to tag the guy as soon as he spawned. And even as parties would get their kill and move on, more would keep arriving so that some people waited for upwards of an hour while those that have the better instant casts tended to get the tag off. When I did the quest on my shaman a couple of weeks ago, it was much more managable, I basically just waited until the horde party tagged him and got him on the respawn. And when I did it on my night elf last night, I basically had Ned all to myself. Borean Tundra and Howling Fjord are effectively deserted compared to their state after the launch.
I do wonder if I'm in some kind of lull between when most folks got their mains to 80 and started working on whatever their consider the endgame, be it full-time raiding or PvP or what have you, and the inevitable decision to level their alts. I know a few people in my former guild were totally uninterested in their alts even when I was leveling mine, and even I have to admit I haven't touched my horde-side characters. (I'm actually surprised by this, as I expected I'd jump right on them.) The fact that we're smack dab in the middle of the December holiday rush might also be having an effect, as people simply have other things to do than play right now.
Still, it makes going through these zones sort of lonely. I actually turned general chat back on last night and no one was talking. No poorly spelled complaints about lag (and to be honest, no real lag that I noticed), no 25 minute rants about anyone's mothers, not even any desperate PuG's looking for a healer with three paladins and a druid in the group. Borean seemed almost deserted, and I quested and leveled through the zone with no one to compete with (which was good) and also no one to group with for Last Rites (which was less good).
Have you been working on your alts yet? Is it 'too soon' for you, are you still on your main or just taking some time to enjoy 80 before moving to alts?