I was mulling over different people's play styles and how things are developing as we move towards WotLK. Some folks I know are trying to get one of each class to level 70 before deciding which to take to 80 first, others aren't.
If you asked me a month ago about Lorienne, I would have said that she was stuck at 65 for ever - I had no interest in playing her because I love my priest too much. Then I started doing bits and pieces with her again and suddenly she's 70.
There is no question in my mind which I'm taking to 80 first - it will be Sephrenia. When TBC came out, she was a new level 60 - all greens and blues, whereas Lorienne was a full epic ex-hardcore raider (and YES, I've still got all her gear in the bank). I started with Lori first in Hellfire Peninsula, but found myself wanting to play Seph more, so switched to Seph full time. I gave Lori to my son for a bit because he really, really wanted a rogue, but he got bored of her, so she came back to me.
I do enjoy playing my rogue again now, but I don't get the same "buzz" I get from playing my priest. The moves don't flow naturally, I have to work hard to play her fully, but with Seph it almost feels instinctive - I naturally "know" what buttons to hit, what spells to use, how to react in most situations. It can't be because I've played her more, because I still feel like I've done more "serious" playing with Lori. I just seem to be more in-tune with the priest.
Maybe she's more like the "real" me - I love to look after people, I'm happy in the background, keeping things moving, supporting those in the limelight.
I have numerous alts and, for example, would love to have a level 70 Druid to play and maybe a Shaman, but I just can't face levelling them. I would spec them healing anyway.
My son is similar - he has loads of characters, but always seems to return to his Orc Warrior - he can't keep away. Barkie, my husband is the same - he has a level 70 druid that he absolutely loves and a 70 warlock that he plays every so often. He seems to quite enjoy his level 40 Shadow priest, but would prefer 3 druids - a tree, a chicken and his cat/bear.
I have friends who have at least 6 level 70 characters and they enjoy playing them all. Maybe the deathknight will fill the "gap" in their characters, I'm guessing that it won't. To me it seems you have a class that is "yours" or you are a nomad, playing all classes and not finding one that perfectly suits you.
So - have you found your ideal partner, your one true love, or are you still looking for Mr (or Mrs) Right?