I've been trying to count, I believe this happened to me with a total of three different girls when I was in high school.
Yeah, I also did it to one girl while I was in high school. I had intended to ask her out, so we got close and everything, and then I found out this other girl liked me, so I pulled a 180 on the first girl and gave her the whole friend thing. The end result was that the girl I ditched the first girl for ended up liking someone else better, so I got ditched and ended up with nobody. Leading on and ditching the first girl is probably the worst thing I've ever done in my life, and I still feel horrible about it (this was like five years ago).
As for you Wolfy, all I can really say is time heals all wounds. I graduated high school in 2004, so I rarely if ever see any of these people I've been talking about anymore, but we still talk on MSN and such. I had a class in my first year of University with one of the girls that I liked but only liked me as a friend, and the girl that I ditched, and we all sat together and got along well. These kinds of things tend to just kind of fade away as everyone involved moves on. I know, it sounds impossible right now. If it'll make you feel better I can dig up some chat logs from a couple of the times I was crushed by getting close then getting friended ;).
P.S. My current girlfriend I guess I finally got it right, after screwing things up with all the previous girls I mentioned. We met, hung out a lot for like a week or two, and I quickly asked her out before the whole "friend" thing set in. Our 3 year anniversary is in June.