My roommate moved out of my/our apartment last weekend. We shared the unit for about 40 months, although my primary residence was in Montreal for 12 of those months.
I think lots of people have roommates solely for financial reasons; someone to help pay the rent. I was pretty lucky that my roommate was a close friend. He was also about the same level of cleanliness and a non-crazypants. My sister once rented an apartment with a friend of hers, but the roommate relationship deteriorated quickly and they had to break our of their lease within 6 months of signing it. Having some common ground with a roommate makes a big difference. It's been fun coming home, making a quick supper then chillaxing with a beer over a Blue Jays game or a few episodes of Metalocalypse.
I love some aspects of living alone - organizing things however you want, postponing dishes as long as you want - but I miss the reliable human interaction already. Despite the benefits, I'm just not a fan of inhabiting a space by myself.
I can survive alone just fine (as I did in Montreal) and Robyn will be moving in soon enough (yay!). I am looking forward to that. A significant other trumps a roommate in the sense that everything is "ours". There are still personal boundaries, but there is no "my room" and "your room", or no "my carton of eggs" and "your carton of eggs".
Of course, I hope we don't stay in the McPherson apartment for too long. It's just... crummy.