Growing up, I was happy to see Iowa State do well, but wouldn't call myself a big Cyclones fan. I always did enjoy watching Johnny Orr's basketball teams, though, and thought very highly of players like Barry Stevens, Jeff Hornacek, Jeff Grayer, Tom Schafer (Anyone besides me remember him? He had one heckuva senior season!), Lafester Rhodes, and Mark Baugh, among others.
Then I went to college at Iowa State, and absolutely loved the experience. Plus, I got swept up in the excitement of sitting in the student section of Jack Trice (then still known as "Cyclone Stadium-Jack Trice Field") and Hilton Coliseum. I went from being a casual fan to a die-hard fan very quickly, and have been a huge Cyclone fan ever since.
On a tangential note, I find it interesting how many posters here seem to include mentioning their hatred of Iowa as part of their deeply-ingrained identity as a Cyclone fan. Knowing many Iowa fans as I do, I can guarantee you that very few of them would mention Iowa State if a similar thread were posted on one of the Iowa message boards.
By no means am I trying to defend Iowa fans, because I know plenty who would say eye-rollingly stupid and annoying things in response to a question about how they became fans of the Hawkeyes. I just know that few would even mention their hatred of the Cyclones in a discussion about how they came to root for Iowa. This isn't meant to pass judgment in any way, just an observation about the difference in the psychology and culture of the two fan bases.