As someone working towards being a dog trainer I sit and ponder the relationships people build with their dogs, and more than that, why people choose the dogs they do. Something that I've noticed is when many people meet Guinness, they say they want a dog just like him because he's so pretty, he has so much energy and life, he's so smart. For the most part, it is my humble opinion that those people need to get their heads out of their respective asses.
Here's the thing, people: you don't want a smart dog. You want a dog that's well-behaved, not more demanding than you're willing to give, and you mistake my awesome dog as the embodiment of those qualities. However, what most of these people aren't considering is the sheer amount of work necessary to make Guinness the dog he is - the training, attention, and sheer amount of exercise necessary to content Guinness vastly outstrips the needs of most of the dogs you meet in a day.
More than anything else, this is a factor of breed. Guinness is an Australian Cattle Dog/German Shorthair Pointer mix. It's hard to come up with a more energetic, intelligent breed combination than that and for the average owner, that is way too much time and responsibility to fit into their schedule.
As a for instance, I recently spent about 6 months living with a small mixed-breed terrier, and Guinness. If you were to leave Solomon to his own devices, he was perfectly content to lay on the couch and snooze for probably 15 hours a day. You could cook a meal, clean the house, and all the while Solomon was content to simply chill out. Meanwhile, if I decide to go into the bathroom, when I open the door, Guinness will be laying just behind it, staring intently at the door waiting for me to come back out. If I don't walk him, he starts climbing the walls. He just runs on an entirely different octane than the average dog. It's like trying to make a Ferrari your running-around car to pick up the kids - that car is just better suited to an owner who will realize the full potential locked up within.
Additionally, in the times where I'm NOT walking, playing with, training, or otherwise actively engaged with Guinness, I have to provide for his entertainment. Not in an effort to spoil him but rather because if left alone too long, Guinness will invent his own amusements. For many dogs this includes digging, barking, becoming escape artists, and a number of pastimes that will make the owner regret they ever thought a dog was a good idea.
However, for the prepared owner, an extremely intelligent dog is a very rewarding, engaging experience. I rarely have as much fun as when Guinness and I are out on the trail alone together hammering out another loop. Or when I'm teaching him a new command (for instance, he finds my keys on command, is aware enough of sled dog commands to run alongside my bicycle, and high fives on his right foot, shakes with his left). So for me a dog of such intelligence is a good idea. But most people need to VERY STRONGLY consider themselves before they get a dog they can't handle and it ends up in the shelter system.