When would one term be more appropriate then the other?
Como estas tu? vs. Como estas?

Gringo1
December 1, 2011

Cristian-Montes-de-Oca
December 6, 2011
Hola GRINGO1.
Both expressions mean the exact same.
The "tu" on the end of ¿como estas tu? its already implied.
You can find the clue in the way the word "estas" ends...for example.
Yo estoy
El/ella está
Tu estas
Ellos estan
Nosotros estamos
As you can say the verb "estar" changes depending on the person...so you CAN`T ask "Como estamos tu?"...cause "estamos" is only used with "nosotros" or we. In this case the correct question would be "¿Como estamos nosotros?" but again, without the "nosotros" the question will still make sense, again, it is already implied :)
I hope i was clear!
Mucha suerte, saludos desde México :)

Gringo1
December 8, 2011
Muchas Gracias!

Raymot
December 9, 2011
Gringo, you'd use tú for emphasis, since there is no ambiguity here.
Imagine this dialog:
A: Hola, Come estas?
B: Bien. Como estas *tú*?
It would sound mechanical just repeating the same phrase. In English, the emphasis might be like this:
A: Hi. How *are* you?
B: Fine how are *you*?
The stress placed on *you* in the reply is the same using *tú* in the first dialogue.

Gringo1
December 9, 2011
I just had an "ah ha" moment Raymot, thank you!

Cristian-Montes-de-Oca
December 13, 2011
Excelente!!! saludos desde Mexico amigos mios!