If all my friends are busy and I really feel like going out, I'll go solo. I've only done it a few times, and it's been fun. I go to a local bar that I know the staff, and I gotta tell ya, it's left some good impressions on some ladies when they see all the bartenders know me and comp'ing my drinks. A few times I see people I know and I talk with them a little; one time, one person asked "who I was here with" and I just said my buddies aren't here, but that person is a complete tool anyway--in general, you won't get that question, especially not from women.
I was out solo on Friday after a long work week and scored the number of the hottest girl at the bar--and she approached me! I was at the bar talking to the bartender, she came up and ordered a drink, and just started a conversation. After like 5-10 minutes, she was like, well it was nice to meet you, my friends are over there signaling to me (she points), but I'm sure I'll be back. I said I probably will be gone, but give me your number and we should do something later. Easy as pie.