You can also unlock new dogs wirelessy via other owners of Nintendogs.
Say you brought your DS with you to the store (turned on of course)...if someone else had their DS on with Nintendogs in range, your puppies can "visit" each other, thereby unlocking a new breed in your game (if the visiting puppy was not yet unlocked". Items can also be shared this way. Mind, you don't need to have physically met the person or any of that...you might not know this exchange occured until you opened up your DS again.
The above is a true story BTW...the above account was posted in the Nintendogs thread on the GAF board.
So this game has sold well over 100,000 copies in the 4 day period. In the same period more than 70,000 DS' were sold as well.
Color me impressed...I certainly won't be discounting the power of "kawaii" in the future...