I had no problem leveling from 70-80 in the first week of the release when everything was being farmed to nutters. (one quest really got on my nerves tho, was a colllection quest of shields and weapons in Dragonblight. And I had mucho competition. ;<)

Overall though, collection quests are very doable, nothing in northrend seems to have too terrible droprates.

I did all quests in borean, howling and dragonblight. Then did some stuff in grizzly (about 25-30 quests) but got annoyig, went zuldrak and did the arena and like 4 quests but hated the zone, so went to basin and I totally loved basin, did all quests there were there. Then went Storm peaks and did the line up to sons of hodir and some other quests here and there and some questline in icecrown leading up to a blue caster shield reward. And then I dinged 80.