I'm going with the general consensus that Dogmeat was a novelty, he wasn't like Ian or Tycho that were actually useful in a practical sense (although most people would argue against Ian).
However, he could be a life saver in the early game, and my 'Dogmeat Must Live' runs made me feel for the little pooch.
He was an incredible nuisance in Fallout 3 though, did shit damage, soaked up a shitload of damage, hell, I was playing on Very Hard and he soaked everything up like a sponge, it took concentrated fire from two Super Mutant Masters and a horde of Brutes to put him down, and he still lasted about 30 seconds.
The greatest crimes can be contributed to his acts of getting in your fucking way during VATS, he loves jumping erratically and screwing up head shots by pouncing on people's skulls.
Also doorway blocking, I can't believe they didn't realize that having to slowly push your way out of a passage would be immensely annoying, it's not so difficult to program AI that walks in a different direction when you get near them, it's even worse when it's Dogmeat and you sometimes get stuck and wonder "What the fuck is blocking me." Only to look down and see the smarmy little bastard.
Pushing idiots out of the way in FO1 (which was terrible) and FO2 was annoying, they really should have fixed that.