I just have one. Most of the time, I'm very content with it.
He's like my best little friend - that typical "human/dog bond" you see in the movies (LoL- think about it, most dog-related movies, they only have 1 dog) and I must say it's pretty easy. I like spoiling him, he gets plenty of exercise and doggy socialization, he goes most places that he can with me including family get-togethers, running errands, etc. All in all, I like having 1 dog but I miss the aspect of him having a buddy to play with inside. My moms dog lived with us until she died and he lost his play buddy.
But we still do go to my dads house once or twice a week where he gets to play with his dogs. Basically, it was nice having the playmate but not the responsibility.
I know I'll get a 2nd dog eventually and I think I'll just know when it's time. I start dogsitting tomorrow for 4 nights for a pup around Jackson's size so I guess it will be a good trial-run.