I have 3 and this is what I have learned from my guys...
Pros
More play time.
More love from the dogs.
They keep eachother entertained.
More body heat from the dogs.
The joy of seeing them playing is the greatest.
They are like children. You always have an adventure.
When 1 is sick the others talk doggie to them and sniff them back to health.
Cons
I have 2 girls so I have to say, an all out barking match for the male's attention.
When 1 is sick and at the vet's the other's mope around the house until the sick 1 is home.
POOP, POOP and more POOP!!!!!