I used a hybrid of a blood tanking and blood raid DPS spec for most of my leveling, only going down unholy to get the "on a pale horse" talent. The talent affects flying mounts too I believe, and you're going to want to go unholy anyway for some of the useful talents there.
Blood DPS/Tank specs have the advantage of using Death Strike as their primary Unholy+Frost attack for big hits and big self-heals. If you spec properly, death strike will turn your frost and unholy runes into death runes, so if/when you reach your 2nd rune usage rotation, you can just spam heart strike (think blood strike, but better damage and hits 2 targets ala cleave) for even faster grinding.
You will find however that most servers have a TON of DKs and Paladins in the end game, so finding raid groups may become difficult unless you're a really good tank.
Edit - as for weapon upgrades as you level, there's the
void axe you can easily get from the ring of blood quest chain (I think you have to be 63 to do this) that can easily carry you up until you hit 68, then you head to borean tundra and do the quest chain up there for another great leveling weapon (
This axe specifically). That can suffice until you get a better one through random LK dungeons or the Amphitheater of anguish in Zul'Drak (
This guy).
By the time the De-raged war axe starts to let you down, you should be in normal icecrown 5-man instance runs, or other heroics, where you'll get into IL200 blues/epics. From there, it's just a matter of getting lucky with drops and instance selections.
