Just once, though I didn't know it at the time. The friend doing the setting up had given me some other pretext for why she wanted to come by to see me.
When she showed up, I had another friend over and at the time I was in the basement finishing up the soldering on some electronics prototype, so I asked him to answer the door for me.
He didn't come back.
Turned out that she assumed he was me, confessed that it was a "set up," and invited him out. Off they went, and I'm not sure how long things went on before he told her who he was.
They did hit it off, but it didn't last. Not a surprise; friend #2 has always made it a habit to bail out of anything when it starts working: as soon as he gets settled in an apartment, he moves; if he gets a promotion at a job, he quits; if he gets along with a partner, he breaks up. Nice guy, very funny and smart, but he's only happy when things are going wrong in his life.