It's got some problems in individual rankings and close rankings (i.e. 3rd vs 4th) because the tests they used were not very comprehensive and didn't take into account the different breeds' skills.
But there's really not much question about the extreme ends of the list. Border Collies are scary smart (to the extent that you DON'T want one if you're not an experienced dog owner and dedicated to LOTS of active dog sports), and Afghan Hounds are so stupid it's a wonder they remember to breathe. A school friend of mine bred and showed Afghans, and I have never seen so much stupidity concentrated in one place in my life.
My inclination would be to rate the guide dog breeds (Shepherds, Labs, Goldens) as the all around smartest in terms of being most useful and adaptable. They have to be to be guide dogs. Border collies would make lousy guide dogs because they are obsessive-compulsive and hyperactive as well as being smart.
“My inclination would be to rate the guide dog breeds (Shepherds, Labs, Goldens) as the all around smartest in terms of being most useful and adaptable.”
Yep, I totally agree with that. Retrievers are just the best dogs....
I've got one. He's smart, but not very scary. He isn't quite full grown, and we don't do dog sports. Instead, he has a slightly older Australian Shepherd as a workout buddy. A few hours each day running
around our one acre, wrestling, jumping over things, and playing 'bitey face', and add in some help from our pound mutt, and he's ready for his nap!
While still VERY young: 
Gotta be careful who you piss off!
