german shepherd/great dane mix

[wolfsoul]

The two breeds have entirely different energy needs, growth needs, and temperaments/personalities.

Exactly -- these are two very different breeds. It is not fair to the potential owners who can never know what the puppy is going to be like. Great danes are typically fearful/unconfident dogs ---- you mix a fearful dog with a GSD that is typically more aggressive, you may be breeding fear-biters or shy sharp dogs. But it's impossible to tell -- rather than the two personalities mixing you can be getting a GSD temperment by itself or a great dane temperment by itself. It isn't fair to the owners who are only expecting a cute puppy.

[leansnslobbers]

Great danes are typically fearful/unconfident dogs ----

I disagree that it's a typical breed characteristic. The fearful/unconfident danes are the ones who are never socialized properly, or came from a very poorly planned out breeding where temperament was not assessed in the breeding stock.
The GDCA standard for temperament is such:
The Great Dane must be spirited, courageous, always friendly and dependable, and never timid or aggressive.

But I do agree the two temperaments are vastly unique of one another.

[wolfsoul]

I can only base my opinion on what I've seen -- every show I've been at, more great danes have backed off the judge than anything else. Every great dane that comes into the shop is a wreck of nerves. The few I've met who have been confident, friendly dogs have ironically been from the SPCA. Not saying it's a bad thing, I breed Belgians and still admit that as a breed they are shy, aggressive freaks.