Ooh, the talk of friendships among dogs. I love it!
Having a large number of dogs in the home, I have the privelege of watching different types of relationships develop between them, and how complex those relationships are.
Gaci and Shimmer are quite good friends. They snuggle together, they play together, they wrestle together. They groom each other. They sleep together. They do argue from time to time, but what friends don't? 
Tequilah, the Shih Tzu mix, had no real friends until Tikkle (the Pap) came along. Tequilah has always viewed herself as being too good for any other dogs (she was fond of cats though). She does not like our Mini Schnauzers. Every single Mini that comes through the home will get one proverbial nip from her, enough for a good squeal, to let them know that she's not friendly, so don't try to be friends. And then they live in harmony. *G* It's not so much that she dislikes them, as she'll sleep next to them and she coexists well, but rather that she's indifferent and has no desire to play with them.
Contrast that to when Tikkle came into our home - it was love at first site for her. Why, we were not sure as we didn't know how she'd take a new dog. But the second she saw her, Tequilah was in utmost heaven. She learned to PLAY once again, it almost brought tears to our eyes, watching her play with another dog. Tikkle actually had to teach her "how" to play, actually, as she hadn't played with other dogs for a good eight years or so. It was amazing, and it was good for Tikkle too because she was so tiny at the time and had to be careful around the Mini's. I actually took a video of when Tikkle was smaller of the two of them:
http://www.youtube.com/watch?v=nx_7werZZSE
I warn you now, this video is just about impossible to watch without the possibility of giggles, or even outright bursts of laughter. So consider yourself warned if you are attempting to drink any form of liquids.
Their mannerisms are to die for (and the part where Tikkle runs FACE first into a wall is America's Funniest Videos-worthy).
Let's see, other relationships.....Zipper is the guy that everybody loves, and who loves everybody. I'm constantly surprised at the relationship between our three males, because of the simple fact that they are all intact and get along marvelously. Oskar and Poker had a tiny rough patch once Poker developed hormones,but it was only noise and stancing and it seems they have gotten over that. Zipper LOVES his guy friends though. They play like no tomorrow, and when we sent Oskar to his breeder for three weeks to be shown, Zipper very visibly missed him. And even more visibly celebrated when he came back home to us. It was too cute. So the relationship between the three boys is quite strong itself.
Umm....Remi and Phoenix aren't really "friends" with any of the other dogs in particular. They are two of the oldest (Kamara is older than Phoenix though), and they basically spend their days lazing around. Remi is more the "mom" of the group.....she is the official butt-licker (it's the lasting mothering in her from when she had litters....she really thinks it's HER job to clean all the butts, especially when girls are in heat), and she keeps the peace in the home. She will break up any quibbles, protect new pups in the house by discussing "issues" with any rough-playing dogs, and disciplining as necessary, and generally doesn't take any cr*p from anybody. She is a great mediator and often times we leave situations up to her to fix. Her communication skills with the dogs in the home are amazing.
Kamara loves playing with Shimmer in the house. They have great wrestle sessions, lots of noise and bitey face. They don't sleep together much, and don't groom each other much, but they are good for games of play. Outside, Kamara will play with anybody who will play with her, especially Oskar for a great game of tug-o-war, or any of the pups she can entice to chase her.
Umm....Kaper, Xaria, and Poker all grew up together (Xaria is a month older than Poker, who is a month older than Kaper....Xaria was bought from a Canadian breeder, Poker is our Czech import, and Kaper is a homebred girl), so they naturally formed a good friendship with each other. They play together likely most out of all of them. Kaper loves to play with anybody who will play with her, though (even Tequilah will tolerate her, and hasn't given her a nip yet, which surprises us), but overall these three are what I would definitely call "friends" in doggy terms.
Kizmet is a bit of a loner. She likes the other dogs but doesn't really have any close ties to them. She much prefers taking all of "her" toys up on to "her" chair and taking pride in playing with them all in sequence. She's also likely the most laid-back of them all and basically goes along with what everybody else is doing (except during suppertime, during which she reigns dictator of dogs over proximity to the food closet....or so she believes).
I'm not sure here if I've covered everybody, but that's a glimpse into friendships for our dogs. Our dogs meet a lot of other dogs, some of them more than others, but they don't routinely play with any strange dogs since they have so many dogs to play with on their own turf, they think of those guys as their friends. They don't really have any dog-friends that reside outside of the home.