Well, if you're an achievement hound, you head to Shattrath, of course! There you can spend a measly 1200g to get a Haris Pilton "Gigantique" Bag. Then fly to Zangarmarsh and drop 1600g on the Cenarion War Hippogryph. Two achievements in the space of 5 minutes, and it only cost 2800g. Not a drop in the bucket, but certainly more affordable thanks to the increased flow of gold in Cataclysm.
After that, since I was in Outland, I took Aeth out to solo some heroic BC dungeons. She managed the Old Hillsbrad Foothills, Black Morass, and Blood Furnace last night without much difficulty at all. At the end of it all, she had managed to pick up another three achievements. Woot!
Even better, along the way, she gathered about 7k reputation with the Keepers of Time - bringing her almost halfway to exalted, on track to get two more achievements: The Burning Crusader and one more step towards 45 Exalted Reputations.
Reputations aside, last night reminded me how fun doing older solo content can be. As a level 80 arcane mage at the end of Wrath, doing the high-end BC heroics solo was just a bit beyond my reach. Now, at 85, they're doable - still a bit of a challenge, though, especially for a squishy mage.
It's kind of odd, but the elites in the BC dungeons feel a lot like the non-elite mobs in Cataclysm. Their health is a little lower, and in some cases, their damage is way lower. In others, though - here I'm specifically thinking of the Heroic Blood Furnace - the trash mobs are still a challenge, even with the health and damage increases that Cataclysm has brought to the table. It makes me think that a little bit of dynamic tuning might make the dungeons even more interesting for solo play.
Maybe this weekend I'll head to Northrend and see what it's like trying to solo some of the entry level dungeons there, starting with Utgarde Keep. Or get a guild mate to join with me and forma raid group so I can see what Karazhan looks like, now that I'm level mondo. My gut feeling is that, even with the Cataclysm changes, both UK and Kara will be a significant - and very fun! - challenge.