The time between expansions is a great opportunity to change your play style. You can become more proficient with PvP, learn to not stand in fire, or pick up a new class. It can be hard to find guilds to take you in as an undergeared, fresh class player, but things are also a lot more forgiving. You'll be under geared but with everyone else around you rocking some of the best gear in the game, you don't really have to worry about your gear being too huge of an issue.
For me, this is also a great time to switch between overall play styles. Back in Burning Crusade I was a hardcore raider. 25 hours a week of raiding, our guild made it into the top 150 in the world, and I'd tank like an army drill sergeant. When Wrath came around I floundered and had enough, I went down to being "mid core" -- the gray area between casual and hardcore. I'd raid with dedicated groups, but I wouldn't do more than 10 hours a week.
Cataclysm saw me fall entirely into casual land, except near the end when I joined a hard mode raiding guild. At the transition to Mists I once again returned to my casual brothers and sisters and raided a lot through LFR and with friends' guilds. It was a good time, and I've had a lot of fun. But now?
I'm ready to make the switch more intelligently this time. I'm going to go out and find a mid core raiding guild, one that allows me to have fun a couple nights a week while not worrying about racing to the top of the charts. It should be nice and easy transition with another expansion coming through the pipeline.
How do you fall into this? Are you switching play styles? I'm particularly curious if you're moving from PvE to PvP -- with as big of a deal Blizzard is making of PvP, I'm expect a lot of people to pick it up.