So, anybody found a companion NPC yet?? are they deep three-dimensional characters?? do they have an interesting backstory? do you develop a relationship during your travels??

I've had two so far, both joined as you progress through the main story.

(Spoilers below)

The Senchall (spelling) of the brotherhood joined, but she died very quickly.  Then later I had an intelligent super mutant join.  Now he was worth having around.  Can carry a ton so he's great as a mule, and he carries a gatlin laser with unlimited ammo.  Very handy companion.

I found a dog that followed me in the junkyard. he died real quick to cause he just ran at enemies even when i couldnt see em.

"and i never found dogmeat either but if i did i would take him home and tell him to stay"

I completely agree.  I wasted so much time during my first play to find him, and he died so easily.  It would be different if you have some type of control over his attacks.  This time through, he's been sitting at my house in Megaton forever it seems.

my dogmeat is just sitting in my penthouse in megaton, my robot doesnt like him...