With Broken Steel installed, Dogmeat (along with other companions), will gain a large amount of health every time the Lone Wanderer levels up.

If Dogmeat is told to wait in Megaton, and then the town is blown up, Dogmeat will still be alive outside of the Megaton ruins afterward.

In Dogmeat's dialogue, there are 'Scold' and 'Praise' options.

The Puppies! perk has a second, unintended use that makes it possible to recruit multiple followers.

At level 22 (with the Broken Steel add-on installed), the Puppies! perk can be taken so that when Dogmeat dies, a puppy appears at the main door of Vault 101.

He may be found in the area around Vault 101 in this scenario.

Dogmeat can sometimes go missing for long periods of time when asked to find something, sometimes even days.

When instructed to find something, Dogmeat is capable of bypassing locked containers and doors, allowing access to items in containers beyond the Lone Wanderer's ability to pick.

If enemies are nearby, Dogmeat will growl.

Dogmeat can be used to fetch supplies, such as ammunition, chems, food, and weapons.

Shooting Dogmeat in the initial encounter without talking to him will make it impossible to recruit him unless the Puppies! perk was taken.

If the event to encounter him is triggered and the Lone Wanderer does not approach him, he may wander off and be found elsewhere on the map.

Regardless of any other companion or Karma level, Dogmeat can be recruited without incident. He may also be found fighting super mutants in a random place at The Mall.

Dogmeat is found in the scrapyard, fighting off several raiders who killed the dog's prior owner.

Fallout 3 essential companions