I read somewhere that Whitney Houston's producer gives her twice through the whole song, recorded of course. Then they spend the rest of the time singing verses, choruses, refrains, fills about ten times each, while he coaches her through different ideas on each take. That means she literally sings the song 30 times, and she's Whitney Houston.
Of course the producer has a lot of material to sift through, and often, the first one or two takes has the "feel" in it anyway.
I take the same approach to just about any song now. I'll set up a loop on the verse, and keep banging away at it, creating a new track each time in Sonar. When I'm done I'll have about 5 or 6 takes. I may EQ one different and use two together, or solo one and be happy.
I do prefer to do solos as one-shots, but have been known to double or triple them, just in case.