I picked this up in SM. I decided to use it for the first time yesterday on a quest in Strahnbrad, when I would get 3 NPCs attacking me at once. I could fight them without a problem, but the couple extra hits from the dog was helpful. Plus, I noticed if a stealthed rogue was around the hound would alert me by making a noise. I'm an undead mage, and it was nice to have a pet like that, even for just 10 minutes.
What I hated was when the 10 minutes were up; I expected the hound to fade out, but nope. He made a whimpering noise and fell over dead. Kinda bummed me out! (I'm a dork, I get attached to my animals.)