I too, applied twice. The first time I got one interview only (at my state school) That school, in it's rejection letter, outlined what the committee thought were my weaknesses. Basically, as a nontraditional student, most of my hard science classes were taken *several* years prior, so they wanted recent classes. I took 2 classes that summer at a local school with fairly cheap tuition, and 2 classes in the fall. I also retook the MCAT becuase my scores were a couple years old. Having new MCAT scores increased the pool of schools I could appy to (since many want scores only 2-3 years old). I also did better (first time 10-8-10 P second time 12-10-12-Q). I sent my AMCAS in early, and got 5 interviews (though the first was in Feb, so I took 2 more classes in the spring). During this time I worked 2 part time jobs. I was accepted at the state school that inteviewed me twice, where I am now about to start my 4th year.
My school is fairly unique in working with reapplicants, I think. There are several students in every class who applied multiple times. The highest number of attempts I know of is 4. Everyone that I know of who applied multiple times does well (ie they are not at the bottom of the class)
Good luck