Usually, we 3-man instances, and we did plan to do so for the Wrath, but a friend leveled up and wanted to join us, so we're now 4-manning the Wrath of the Lich King dungeons. We started with Utgarde Keep, the nominally 70 instance, but when we moved on to Nexus, we actually found it much easier. Utgarde was doable with 4 except for the last boss which is just not tuned for your run-of-the-mill level 70 tank, and requires much more timing and precision than any pre-70 instance bosses. Frankly, I expect to see the final boss of Utgarde nerfed in the near future. Nexus was another story. It was fun, fast and furious. It changes so much through it different sub-zones, and you really have to learn the instance to do it well.
Last night, Himalountain gained his 70th level, and has joined my other two Horde 70s and one Alliance 70. He then became my third character to get an epic flying mount. This felt like a real accomplishment, but it was nothing compared to what it would feel like, less than 24 hours later, to gain 19 more levels across two characters in one evening! 
