I picked up Wrath at lunch today. After installing I logged on to an 800-person queue for Sargeras. I quickly switched to Skywall, which only had an 80-person queue. I took my hunter to Howling Fjord and did a few of the quests. Then I realized that I really wanted to play my paladin first, so I went back to Sargeras. By this time the queue had grown to 1300 people.
A long time later, I logged in with Coriel and started doing the Borean Tundra quests. Borean Tundra is a bit more crowded than Howling Fjord, but not too bad.
For now, I've decided to go with Retribution and mostly solo. I've decided not to rush to 80, but take my time. To that end, I've turned off Instant Quest Text. It actually does make a difference in immersion, I find. With Instant Quest Text, I barely read the quest, but having the text fade in forces me to slow down, to actually read the backstory behind the quest.