My warlock hit level 70 during one of the horrendous trash pulls in the Auchindoun's Shadow Labyrinth. It took about 2 weeks, a little over but for the first four days my server was unplayable.
I have a few suggestions for those of you who are trying to get 70 in the minimum amount of time spent. First, get out of Hellfire Peninsula as quickly as possible. There are so many people in that zone that I spent way too much time waiting for spawns. Second, unless you are a mage getting powerleveled with the help of a entire guild, quests are the way to go, not grinding and not instances. Finally, my pattern was Hellfire Peninsula to Zangarmarsh to Nagrand to Terokkar Forest to Blade's Edge to Shadowmoon Valley. I did Nagrand first Terokkar Forest was very heavily in use, and I wanted to stay out of that mess. They're about the same level, so it works out. I haven't even been into the Netherstorm area. Why did I skip Netherstorm? I'm a warlock. Shadowmoon Valley is full of demons. I was completely playing to my strengths.
I started The Burning Crusade with about 150 gold on my warlock. I ended with a tad over 1500, not counting green items (sold via my bank alt) but counting all consumables, repairs, flights, and other expenses. Whenever there were quest rewards with no usable options, I picked the 2 handed weapon or the plate armor, those items tended to sell better. Unless you blow all of your cash on tradeskills, you should have basic flying mount cash very quickly.
I managed to find groups to finish nearly all of my group quests on an ad hoc basis. On a couple of quests I got help from in-guild. Now that I've finished leveling, my goals are to finish up all my keys, do some instances, and help the rest of the people in my guild level.