Gotta love it when other people do the work for you, right? Geistig over at Skeleton Jack has a great post on leveling Unholy, for those of you who like the idea of ridin’ around with your best ghoul by your side, being nigh unkillable in an entirely different way, and - oh yeah - moving really fast. Trust the lady, read the post, try the spec if you’re still comin’ up in the world. :)
She mentions it briefly, but I can’t emphasize it enough - if you’re leveling Unholy, take On a Pale Horse. Frankly, I still miss the mounted movement buff today, given the sheer size of Northrend.